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Vented Loops

| Maintenance | October 14, 2015

Vented Loop

Vented loops or Anti-Siphon Valves: are inverted U-shaped pipes with a vent at the top to let air escape. Vented loops are found in toilet discharge lines or in systems which are mounted below the waterline.

 

Vented loops are a necessity for many marine systems to prevent back siphoning . You need vented loops (anti-siphon valves) as part of the engine exhaust system, or plumbing for bilge pumps, or the marine head. The reason you have them is to stop a siphon or backflow of water in the system. With a siphon, the water can travel the wrong way and in the case of a marine head the water can go back into the toilet and overflow it. With an engine the water can flow through the exhaust into the engine causing much damage an flooding.

Vented loops are simple devices and very rarely go wrong, but when they do the results are catastrophic. The boats potentially sinks! Mount the vented loop so it will remain above the waterline at all heel angles. Clean the anti-siphon valve regularly to keep it functioning.

What is a siphon?

I remember siphons from draining a swimming pool as a kid. The pool was on top of a slope so using the principle that water wants to flow downhill. A hose was filled with water and both ends blocked off. One end of the hose is placed in the pool and the other down the slope. Both ends are now unblocked and a siphon is formed resulting in the water flows downhill fully draining the pool.

So how does a siphon work in a boats plumbing system or exhaust system. The diagram right from Jabsco demonstrates the problem.

In top diagram you can see that water will flow into the lower bowl. In bottom diagram the hose has a loop. In this case the hose is filled with water and a siphon is created, so water will still flow into the bottom bowl.

Now if a vented loop is added at the top of the loop the siphon is broke and water will not flow to the bottom bowl.

How does a Vented Loop fitting work?

 

A vented loop is fitted with a one way valve. This permits water to be pumped through the loop. However when the pumping is stopped and no more water is pushed past the vented loop, air is let into the pipes and the water level drops away from the loop on both side, thus preventing a siphon from occurring. The vented loop allows air in but not out.

Detail of a vented loop showing the Duckbill one way valve. The valve allows.

Forespar supplied this diagram of how the vented loop works.

Implication of siphons in boats

Jabsco Vented loop diagram

Obviously the raw water or sea water intake of any boats water system is below the waterline. Also in many cases so are the boats toilets, heads, engines, generators etc. This requires a through hull fitting or seacock to be added to the raw water intake. In case of any failure in the hose or any other part of the water system. The seacock can be shut off to stop water incursion in case of an emergency. However during operation of the boats systems, the seacock is left open. This allows for water to enter the inlet if a siphon occurs. Once the water comes in, a toilet or head can flood.

Boats Heads, Toilets

Marine Heads are often installed below the waterline. Therefore its important to have a vented loop. Most often this is installed on the discharge side of the heads plumbing system. See the diagram courtesy of Jabsco showing the vented loop installed above the boats heeled waterline (if its a sailboat) by 8 inches minimum.

 

Vetus Vented Loop Head

Vetus Vented Loop

If you add or have a Vented Loop in the discharge side of the toilet, add a breather, to vent odors overboard.

I have seen heads & holdings tanks that have vented loops but the vent breather is not plumbed overboard and odors linger below. The picture left shows a Vetus Vented Loop with a overboard breather as part of the package.

 

Engine or Generator Vented Loop

engine vented loop

In an exhaust system without an anti-siphon valve, when the engine is shut down, raw water continues to siphon into the exhaust system until it reaches the same level as the outside, i.e., the waterline. If the engine is installed below the waterline the water will flow back up the exhaust pipe and into the engine itself.

This can be avoided with a vented loop. The vented loop, or anti siphon breaker is a Loop with a small valve that closes under raw water pump pressure, when the engine runs, and opens when the engine stops, allowing air into the pipe, thus preventing the water from siphoning.

Therefore it must be installed somewhere in the raw water line between the raw water pump and the mixing elbow. This diagram shows the vented loop (siphon break) between the pump and the manifold. It is also possible the loop be after the manifold and before the mixing elbow (where the engine exhaust & raw water mixes)

The vented loop which was installed in the seawater cooling system, by the boats manufacturer will prevent a siphon from building. You should find out where it is and add into your yearly maintenance schedule. Check that the valve is clan and working.

Servicing a Vented Loop

Look at your boats systems and find the location of the vented loops. Note their position and add them to maintenance schedule. These should be inspected to make sure they are clean and the valve is seated properly. If the valve is blocked it wont prevent syphoning.

Servicing a Vented Loop

For servicing procedures look at the  Groco installation and service manual.

For servicing of vented loops, Include them in your yearly! maintenance program that include all seacock’s and through-hull fittings.

 

 


 

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Stuffing Box Maintenance

| Maintenance | September 22, 2015

Conventional Stuffing box

Stuffing box maintenance

You are getting water in the bilge and you track it down to the propeller shafts stuffing box (also called stern gland). The stuffing box houses a seal which the prop shaft passes through. Some rudder stern glands work the same. Most stuffing boxes have an adjusting nut which compresses the packing material, controlling the rate of drip.

If adjusting the packing does not fix the leak you may have a damaged or worn shaft. If it’s in any way irregular, pitted, or damaged, the packing will be torn up each time the shaft rotates. If this is the case you can: Replace the shaft, or use a longer or shorter stuffing-box hose to move the location of the packing over to a smooth section of shaft.

1    This article looks at the stuffing box and its maintenance.

Stuffing Box

What does a stuffing box look like? The diagram courtesy of Catalina shows a typical propeller shaft installation with the shaft log and stuffing box. The shaft log is a tubular passage through the bottom of the boat where the shaft passes on its way from the engine to the strut and cutlass bearing. The stuffing box assembly attaches to the shaft log with a length of hose and a pair of hose clamps.

There are 2 types of stuffing box;

 

Conventional Stuffing box

1          Traditional stuffing boxes

Water is required to lubricate conventional packing.

A properly adjusted stuffing box won’t drip when the shaft is idle, but 2-3 drops/minute when the shaft is turning.

 

2          Dripless Shaft Seals DSS

PSS shaft seal

Dripless Shaft Seals don’t drip but still need cooling;

Most DSS units have a small barb fitting on the graphite flange where a hose can be connected to ensure that water is always present. From the fitting, the hose runs either to a place high above the waterline, or, in the case of higher speed vessels, into the engine’s raw-water cooling system.

Passagemaker review of the dripless PSS seal

2    Adjusting a conventional stuffing box

This fairly simple procedure can be done with boat in water.

Stuffing Box diagram

This picture of a cross section of a shaft gland come to us thanks to the Alberg 30 class site.

Notice the “locking nut” and the “adjustable stuffing box nut” in the picture.

Conventional stuffing boxes require water to lubricate the packing. Often you will see water dripping from the box. A properly adjusted stuffing box will have no drips when the shaft is stopped, but 2-3 drops/minute when the shaft is turning.

When adjusting the stuffing box keep in mind that; if the adjustable stuffing box nut is too tight you will burn the packing which can end up with a damaged shaft. If your stuffing box leaks more than 8 drops a minute, it needs adjusting.

Two pipe wrenches are the tools needed for adjusting the stuffing box. Start by loosening the locking nut, this frees the adjustable stuffing box nut. As you tighten the Stuffing Box nut check for leaks while the props are idle. If you notice any dripping tighten the Packing Nut a bit more. Once you stop the dripping tighten the locking nut.

Now you are going to need to check the drip rate with the engine running. You can do this with the engine engaged in forward and the boat securely tied in the slip. If it is more than two drips per minute loosen the locking nut, then tighten the adjusting nut slightly. Access to the engine is critical and you should be aware of the shaft turning. It’s safer to take the engine out of gear, while you’re adjusting the nut. When the drip rate is one or two drops per minute, stop the engine then tighten the locknut.

Final check; As long as the box isn’t dripping too much and isn’t running too hot, you are in the correct range. While you’re at it give threads and nuts a coat of corrosion blocker.

Note; if you use a graphite packing like Gore’s GFTO, it can be tightened until the leaking stops completely but you will need to check the temperature of the stuffing box after running the boat for a while. The packing box should not be hot to the touch. “Since GFO fiber dripless packing is four times more thermally conductive than flax, it needs virtually no sea water for lubrication or cooling. And, because it doesn’t swell or shrink, leakage is controlled and kept to an absolute minimum.”

3          Replacing flax

Ideally to do this project you want the boat out of the water. It’s possible if you’re organized to do a short haul (boat hangs in slings) at lunchtime or overnight. If you don’t have the option the packing may be replaced with the boat in the water, but water coming in may be a bit disconcerting. If you’re organized the amount of water coming in can be handled by the bilge pump.

An excellent article; http://www.pbase.com/mainecruising/stuffing_box

Stuffing box nut

To begin; Loosen the Lock Nut by placing one wrench on the Packing Nut and the other wrench on the Lock Nut. Using two wrenches helps prevent twisting and damaging the shaft log hose.

Removing The Old Flax; Once the Packing Nut is unscrewed from the Stuffing Box, use a pick and carefully remove all of the old packing. It can be difficult to see if all the old flax has been removed and so a dentist’s type mirror can be useful to inspect the Packing Nut. Careful not to score the Packing Nut or shaft.

Next installing the new Flax Packing. A common mistake is winding the new packing around the shaft as a continuous piece. This will not seal properly, instead It must be installed as a series of stacked rings. Usually 3 rings. This requires cutting the packing into lengths that just encircle the shaft with ends touching.

See section 4 materials for length and size.

Placing the new packing material in the nut is a delicate process and it

Adjustable stuffing box nut

requires patience to get the packing right. Start by wrapping the first piece of flax around the shaft snug up against the stuffing box, ensure the 45 degree ends touch. Now slide the Packing Nut up against the flax carefully forcing the flax into the Packing Nut. Once the flax is as far as it will go into the Packing Nut, use a flat blunt object to carefully pressure the flax into the nut. Now install the next flax ring the same way and make sure the 45 degree joint does not sit in the same plane as the previous ring.

When all of the flax wraps are installed in the Packing Nut, begin to thread the Packing Nut onto the Stuffing Box. The Packing Nut will put pressure onto the packing and if it’s too full you may not be able to get the threads on, if you have it right it may take just a little pressure to get the threads. Nest apply more hand pressure to begin to tighten the Packing Nut. When you are max hand pressure, remove the nut and look to see if the flax is seating properly. If it’s OK re-install the Packing Nut and tighten snug using a wrench, back off slightly to ensure that it is not too tight when you first turn the propellers. Now thread the Lock Nut snug against the Packing Nut and tighten using your wrenches.

VIDEO; How To Replace Your Drive / Rudder Shaft Stuffing Box Packing With GFO packing

4          Materials and tools

The Stuffing Box Packing is woven flax or synthetic, squared-off rope like material.

There are two main types of material.

Stuffing box packing

1          Traditional Flax packing; has been around a long time. This grease based packing is very reliable, however if the stuffing box gland nut is over tightened, the flax packing can heat up causing high temperatures and possibly damaging the shaft.

2          Modern Graphite packing; is an excellent a lubricant, reducing the chance of burning the shaft. It is very expensive however.

Sizing and finding the correct length of Flax Packing

Ensure you have the correct size flax packing for the stuffing box, if the old packing is relatively intact you can measure the thickness. The shaft diameter and type of stuffing box should reveal the correct size of the flax. Next you should plan on 3 full wraps of flax around the shaft to fill the Packing Nut.

Now you need to cut the flax to the proper length to fit completely around the diameter of the shaft. Lengths can be cut on the exposed shaft on the outside of the hull if possible. Cut the flax at 45 degree angles like a scarf joint. This will allow the ends to mesh together once the Packing Nut pressure is applied. If you can’t use the shaft you can use a piece of pipe the same diameter as your propeller shaft.

Suppliers; Stuffing-box manufacturer Buck Algonquin (www.buckalgonquin.com).

Packing; Graphite packing http://gfopacking.com/

Tools required; a pair of spanner wrenches or pipe wrenches. Razor knife or razor blades to cut the flax. You will also need a bent ice pick, or a stiff piece of wire bent 90 degrees to remove the flax.


 

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Winterizing

| Maintenance | November 22, 2014

Lowes Antifreeze -50 Degrees F

Laying Up for the Winter

What is most important when prepping for the winter can be summed up by conditions. If it is going to freeze, winterizing the engine and any systems that have water in them, is the absolute minimum you will need to do. Any trace of water can cause havoc whether in an engine, toilet, bilge, outboard, air conditioning or running water systems.Lowes Antifreeze -50 Degrees F

 

If you have the space it is recommended that you remove as much ancillary gear from the boat. This stops the gear from getting cold damp and helps air move around the boat. It also stops certain items getting stolen. Check your insurance policy.If you are having the boat pulled for the winter, most of the winterizing can be done in the water. The engine may be needed to get to the lift so that can be done onshore and engine mechanics have the tools to winterize on land.

Below is a fairly comprehensive list of projects that will help you in the spring. These are fairly general projects. If you are unsure about a particular system you should consult an expert at your boatyard.

 

Laying Up for the Winter

Antifreeze

Marine antifreeze comes in three different temperatures, -50, -60 and -100. At these temperatures the antifreeze will solidify. Glycol content increases from 30% for -50 to 60% for -100.

Propylene Glycol is more environmentally friendly. Do not use automotive type antifreeze, as they are toxic.

Topics include

 

    • Boat System Winterization
    • Inboard Engine
    • I/O drives
    • Outboards
    • Fuel tanks
    • Ventilation
    • Onboard Systems
    • Onboard Water systems
    • Seacocks
    • Empty Bilge
    • Electrical & Batteries
    • Electronics Systems
    • Deck gear
    • Sails & Rigging
    • Steering Systems
    • Cleaning the Boat

FULL ARTICLE HERE

 

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Captain John’s boat brite

| Maintenance | September 2, 2014

Boat Brite

Captain Johns Boat Brite is for removing staining from fiberglass hulls caused by algae and brackish water. It works by spraying the Algae & Waterline Stain Remover onto the fiberglass surface, then just after a few seconds, simply wipe stain away then rinse with water.Boat Brite

The picture is of a boat which is dry sailed but had been sitting in the water for a weekend. You can clearly see the staining from the brackish water, with a cleaned area in contrast to the stained fiberglass. Watch the following video of this hull being cleaned.

Apparently Boat Brite is bio-degradeable, non-toxic and safe for the environment. This comment from Practical Sailor; “The most eco-friendly product tested was Captain John’s Boat Brite Algae and Waterline Stain Remover”

Boat Brite is expensive at $20 for 32oz, but works quickly and your conscience is clean.

Boat Brite waterline Stain Remover may streak antifouling paint but will not remove paint or compromise its performance.

Captain John’s Boat Brite Algae and Waterline Stain Remover does removed wax, so following with a quick cleaner-wax will help keep the stains from coming back quickly.

Full article and Video

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Weld Mount Fastner System

| Maintenance | August 18, 2014

If you ever find a situation where you need to fix something to the boat but do not want to drill a screw hole or cannot due to the thickness of the panel or

maybe there is not enough room, then Weld Mount will come to the rescue. Weld mount is a two part acrylic glue which dries in 2 minutes and is used to attach any one of the specialty designed fasteners to the hull, deck, nav station or anywhere onboard.

The Weld mount system

” Weld Mounts array of fasteners ” “

I watched Electronic Marine in Annapolis fit out an electrical panel with Furuno Electronics without actually drilling a hole anywhere. They use a combination of weld mounts wire ties and stainless studs to attach cables and the electronic boxes. The studs have flat round bases, which glue onto the surface and then you can attach an instrument and secure with the nut. All you need to do is hold the stud in place for a couple of minutes.

Manufacturers Contact Weld Mount System;

 

Adhesively Bonded Fasteners

The Weld Mount System is a unique line of fasteners designed to be adhesively bonded to almost any surface, elimintating the need for drilling, tapping or welding.

Weld Mount Advantages for Composite Construction:
Eliminate drilling into composites exposing the core to moisture.

    • Eliminate the need to use blocking to mount components saving weight & labor costs.
    • Eliminate inadvertent drilling damage which causes expensive repair and delay.
    • Can be mounted in difficult locations where tools and/or people have poor access.
    • Neat and clean installation ideal for last minute changes and additions.

 

 

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Gelcoat Maintenance

| Maintenance | April 22, 2014

Sgelcoat maintenance & reconditioningpring time is when most people are getting their boats ready for the season. If you haven’t already you maybe considering buffing and polishing the hulls gelcoat. This is a very popular spring activity and walking around the boatyard the other day, I could see many buffing machines at work both by professional and by Boat Owners.

Buffing can be a simple maintenance task using a light grade compound or a complete restoration using a heavy compound and even wet sanding to bring back a heavily oxidized Gelcoat. You can wipe your hand over a badly oxidized hull and see the results on your hand.

By buffing and adding layers of protection you not only make the boat look nice and shiny you are keeping those UV rays at bay and adding longevity to the hull.

So how do you bring back your gelcoat. Hand buffing can be extremely time consuming and exhausting. So a buffing machine is in order. Next is the choice of pad and buffing compound.

Gelcoat Oxidization

Hull and Deck Gelcoat surfaces suffer from oxidation due to the sun’s UV rays. This is especially the case for colored hullSabre 42 dark blues. Oxidation on Gelcoat leaves a chalky residue.

The picture of a dark blue Sabre 42 shows a typical situation for a dark hull. The transom which has more direct exposure to the sun has dramatic fading and oxidization while the topsides are only slightly faded. The good news is that this is not irreversible. The color can be brought back but it is time consuming.

Looking at the Sabre 42 pictured I would say the transom needs fully restoring, while the topsides just routine maintenance.

I would use a milder compound on the hull as its only slightly faded. I would then try it on the transom, but If the color does not come all the way back you should try a coarser compound. This transom is just faded and chalky due to the sun so it does not need wet sanding.

If you have a scratched and very heavily oxidized Gelcoat you might have to resort to wet sanding. This can be delicate as gelcoat is only so thick. Sanding should be a last resort only when buffing alone wont remove the scratches.

More on Gelcoat maintenance

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Space Dryer

| Maintenance | March 13, 2014

H20ut space dryer

Dehumidifiers; Boats are wet and especially when they are buttoned up in rainy and cold damp conditions. Because if this we are always interested in dehumidifiers and when the Space dryer from H20ut came to our attention we had to get one.

H2Out Space Dryers come in several sizes but they all are cylindrical stainless containers, containing Desiccant. The space dryer is simply placed in the area in need. The space dryer goes to work immediately and will last for some time. Once the Desiccant has reached its capacity it turns pink. No need to worry as the Desiccant is rechargeable, by placing the canister in an oven and when it turns blue again its fully recharged. The Desiccant is nontoxic, and noncorrosive.

 Testing the HD309 Space Dryer

The HD309 space dryer has a coverage area of 800 cu ft. I placed the space dryer in a J/24 which has a small cabin of around 350 cu feet.

The dryer worked very well. The air after a few days was very dry and there was no condensation on the underside of the deck. Previously to the Space dryer there was condensation drops hanging from the underside of the deck due to wild fluctuations in outside temperature. The SD309 is the most popular of the space savers, but I think too big for the J/24 cabin volume. Even after 2 weeks the space dryer was not even showing any signs of being at capacity, so there was no need to reactivate.

The conclusion and our view of the Space Dryer is that the small portable rechargeable cylinders work very well and are suitable for placing in several places onboard to keep condensation down.

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Canvas Maintenance

| Maintenance | March 1, 2014

Dodger & Bimini

Most boats have some sort of Canvas on deck, be it a Bimini, Dodger, or Sail Cover. Canvas just like any other surface on your boat needs regular cleaning. But even with the best maintenance after a few years the waterproofness of your canvas will wear away. No need to worry as you can reapply the waterproofness with a spray coating.Dodger & Bimini

There are many fabrics on the market but the most popular is Sunbrella woven acrylic fabric. Scroll to the bottom of the page to read Sunbrella’s instruction on maintaining the canvas. Glen Raven manufacturer of Sunbrella recommends 303 High Tech Fabric Guard™ as the preferred re-treatment product.

When cleaning Sunbrella always use a mild soap like Ivory snow, or woolite. Keep the water cold to Luke warm not hot. Before you start clean off loose dirt and remember if done regularly you won’t have lots of dirt to clean. Once the loose dirt is removed use a soft brush to brush in the cleaning solution. Rinse with fresh water and then air dry. Once dry you can apply the 303 or other protectant.

If you have windows make sure the 303 does not get onto them. The best bet is to cover the windows with paper towel so the spray does not get on them.

Full Canvas Maintenance article here

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SeaDek EVA foam non skid

| Maintenance | February 20, 2014

SeaDek

SeaDek EVA Foam non skid

SeaDek is made from thin EVA foam which is UV stable and is easily maintained and stain resistant. Not only does it give you a non skid surface it is soft to touch and if you fall or rub your knee on it it wont hurt or scrape. Its a bit  like neoprene to the touch and compresses when a load comes on it, so impact is softened.

There are more advantages; SeaDek’s impact absorbing surface lessens fatigue. Many powerboats use it under the helm station so the drivers feet are cushioned. Cockpit coamings are also a favorite as leaning against SeaDek is more comfortable than a hard gel coat surface.

For more click here on SeaDek surfaces

 

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Spotless Stainless

| Maintenance | February 1, 2014

Spotless stainless

spotless2

Spotless Stainless

Spotless stainless is a slushy paste that removes rust stains from stainless Steel. This is an invaluable product for a boater as stainless is a very common product, but tarnishes easily making an eye sore. Boat equipment made from stainless include most pulpits, lifelines and stern rails, deck hardware, hatches and ports, windlasses and steering systems etc. In other words a lot of stainless can be found onboard.

Spotless Stainless;  is not a polish but reacts with the rust. And after it is washed off leaves a protective film.

Our test showed great results as you can see from the picture. It works so well you should thoroughly rinse off any excess paste.

Results

Without any real preparation other than the fitting was dry Spotless stainless was brushed on and after 30 minutes the fitting was washed off. The fitting looked much better, but some of the heavy rust deposits around the central pin were still there.

Full article here

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Boat Winterizing

| Maintenance | October 19, 2013

Laying Up for the Winter

 What is most important when prepping for the winter can be summed up by conditions. If it is going to freeze, winterizing the engine and any systems that have water in them, is the absolute minimum you will need to do. Any trace of water can cause havoc whether in an engine, toilet, bilge, outboard, air conditioning or running water systems.

If you have the space it is recommended that you remove as much ancillary gear from the boat. This stops the gear from getting cold damp and helps air move around the boat. It also stops certain items getting stolen. Check your insurance policy.

If you are having the boat pulled for the winter, most of the winterizing can be done in the water. The engine may be needed to get to the lift so that can be done onshore and engine mechanics have the tools to winterize on land.

Below is a fairly comprehensive list of projects that will help you in the spring. These are fairly general projects. If you are unsure about a particular system you should consult an expert at your boatyard.

Laying Up for the Winter

Marine antifreeze comes in three different temperatures, -50, -60 and -100. At these temperatures the antifreeze will solidify. Glycol content increases from 30% for -50 to 60% for -100.

Propylene Glycol is more environmentally friendly. Do not use automotive type antifreeze, as they are toxic.

Boat Winterizing full article

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Marine Caulking Products Guide

| Maintenance | October 18, 2013

Marine Caulking Products Guide

Leaks can be just annoying, or cause structural damage and even lead to sinking . Despite this leaks are very common and can be found on new boats and old boats alike.

This page is dedicated to caulking products. Choosing the right sealant or caulk to bed fittings is confusing and a walk down the isle at the store leaves you wondering what do I need. A sampling of caulking materials found at the chandlers, include fast and slow cure, permanent or removable, polyurethane adhesive/sealant, polysulfide bedding compound and silicone, as well as glazing adhesive, teak deck caulk etc, too many choices.

Properties of Sealants

Curing;

Curing may take days, depending on the material, air temperature humidity-most urethane sealants actually cure in the presence of moisture, which is why they’re excellent for emergencies underwater repairs. Many caulks are moisture cured; some are 1 part slow Curing times 2-14 days others are 2 part fast cure.

Stretch or Elongation;

Elongation is a measure of Stretch. The higher the stretch the better the caulk bond will hold up. Caulk can have between 100 and 800% elongation and more at break.

Consistency

; Liquid, paste or tape

Adhesive by the numbers

; This chart gives you an idea of the difference between the types of major caulks. These numbers are a rough guide as products vary. Bear in mind 700psi could tear apart fiberglass when removing a fitting. Adhesion = peel strength, strength = tensile strength

Full Article “Marine Caulking Products Guide” here

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Understanding Bottom Paint

| Maintenance | April 5, 2011

This is the time of year where you are planning your next boating season and before you launch your boat, you more than likely will be repainting her bottom. So what to use? Today paint choices are abound, but the main choice is between;

Hard antifouling

Biocides/toxins

; When a bottom gets fouled the first sign is a slime covering the bottom called biofilm, which then leads to algae growth which in turn leads to barnacles and other creatures attaching to the bottom. To combat this Bottom paints contain biocides, cuprous oxide being the most popular, which are released at a controlled rate.

Level of Toxins

Hard paints contain varying levels of biocides which are released slowly on contact with water. Ablative paints generally contain lower levels of toxins but they are released at a more steady rate as fresh paint is exposed. In addition to Cuprous Oxide many paints now include a slimicide to prevent growth of slime. Slimicides can be identified by the names; Irgarol, Biolux by Interlux, and SR Slime Resistance by Pettit.

Cost of bottom paints ;

Full Article Bottom Paint Guide

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