1 1/4" through hull, what the heck?

[Ambler]

Originally Posted by Cadence

If it ain't broke don't fix it. Send it back.

My thoughts on through hull and valve fittings one size bigger than required for an cooling water">engine cooling water inlet.
Your impeller will work harder if there is restricted flow from a barnacle, oyster or even a build up of antifouling paint in the through hull fitting. Who hasn't seen that when hauled out?

My boat already had the bigger through hull fitting and the boats first owner ran a marine engineering business in Sydney.

Issues arrising from restricted flow - an impeller vane can break away from working harder than it should and age, it will usually block part of a tube stack cooler. Not good as it impedes the flow again and lowers the cooling efficiency.

[Cadence]

Originally Posted by Cadence

I feel sure through hulls are like pipe, inside dia. is the specified size. Then you may have SAE or metric to consider?

PS, pipe (tampered) or strait thread,

[KP44]

Originally Posted by Cadence

If it ain't broke don't fix it. Send it back.

If it is not broken, don't fix it. Very true. But we must keep things ship-shape.

Little jobs become week-long jobs. But we learn from every job and what took a week will only be two hours next time.

I saw 5200 mentioned in this thread and want to say that there are few places on a boat where 5200 is appropriate. There are better beddings and bonders.

[Cadence]

Originally Posted by KP44

If it is not broken, don't fix it. Very true. But we must keep things ship-shape.

Little jobs become week-long jobs. But we learn from every job and what took a week will only be two hours next time.

I saw 5200 mentioned in this thread and want to say that there are few places on a boat where 5200 is appropriate. There are better beddings and bonders.

If it ain't broke don't fix it, was colloquial.
I meant, unless there was a need to upsize the through hull why get into a larger project than necessary. Replace it with a like for like product.

[KP44]

Originally Posted by Cadence

If it ain't broke don't fix it, was colloquial.
I meant, unless there was a need to upsize the through hull why get into a larger project than necessary. Replace it with a like for like product.

I meant to say the same. Don't mess with something that works. (And never make a hole in your hull any larger than absolutely necessary.)

[CassidyNZ]

Originally Posted by a64pilot

I agree with this, to make the hole larger I would bond a piece of wood to the inside of the hull to give the hole saw something to drill into.

It appears the OP has made the decision to return the larger skin fitting but just for the record . . . .

Placing a hole saw the same size as the existing hole onto the same mandrill inside a hole saw of the new required size (a thin spacer may be required depending on the individual saws) will enable accurate resizing of the hole. The smaller hole saw will centre on the original hole before the larger one starts cutting.

[Red Sky]

Originally Posted by CassidyNZ

It appears the OP has made the decision to return the larger skin fitting but just for the record . . . .



Placing a hole saw the same size as the existing hole onto the same mandrill inside a hole saw of the new required size (a thin spacer may be required depending on the individual saws) will enable accurate resizing of the hole. The smaller hole saw will centre on the original hole before the larger one starts cutting.

Thanks CassidyNZ, exactly what I was looking for. Just went to the garage to test it. A simple yet brilliant solution.

[Cadence]

Originally Posted by Red Sky

Thanks CassidyNZ, exactly what I was looking for. Just went to the garage to test it. A simple yet brilliant solution.

I'd agree! I would not have thought of using it as a pilot.

[Bigjim]

My concern about using a pipe that is bigger is that engines are usually designed for specific dimensions. For example, the exhaust system of most cars is designed to produce a specific back-pressure to the engine. If you remove the exhaust or use one that's too small or too big the engine will not operate properly.

The water intake is about three feet from the water inlet in the engine and pump. So it has to suck water up into the engine before it can pump it through the engine. If the inlet is too big I'm concerned that the pump will have to work harder than it should have to to produce the necessary suction. Over time it will stress the impeller more and it could fail sooner.

I may be over thinking it, since it's only 1/4 inch wider.

[Ambler]

Originally Posted by Bigjim

My concern about using a pipe that is bigger is that engines are usually designed for specific dimensions. For example, the exhaust system of most cars is designed to produce a specific back-pressure to the engine. If you remove the exhaust or use one that's too small or too big the engine will not operate properly.

The water intake is about three feet from the water inlet in the engine and pump. So it has to suck water up into the engine before it can pump it through the engine. If the inlet is too big I'm concerned that the pump will have to work harder than it should have to to produce the necessary suction. Overtime it will stress the impeller more and it could fail sooner.

I may be over thinking it, since it's only 1/4 inch wider.

You are correct Jim.
My set up uses a 1"1/4 skin fitting and ball valve then a reducer to a 1" pipe all the way to the impeller via an internal strainer. All fitted below water level I might add.

[CassidyNZ]

Originally Posted by Ambler

You are correct Jim.
My set up uses a 1"1/4 skin fitting and ball valve then a reducer to a 1" pipe all the way to the impeller via an internal strainer. All fitted below water level I might add.

Therein lies the answer.

If the pump was pulling a head of 3ft then increased pipe diameter may play a negative part. But when the whole system is below water level, the pump is simply moving water. Disconnect the pipe and water will naturally flood into the boat so the pump is not required to work any harder. In fact I would suggest the converse is true, a larger diameter pipe would provide more water to the pump.

Well, at least that’s my logic. YMMV.

[NorthCoastJoe]

Keep the larger one, I taught pumping in the fire service. Larger intake size means less work for the pump. You can use a step drill to go larger on the hole size, boat yards should have them.

[cottonsail]

Do I really need a raw water screen?

[Wireless1]

Originally Posted by Bigjim

I'd probably not want to enlarge the hole if I don't have to. So, I guess I'll send it back.

It’s easy to make the T-Hull hole bigger. You don’t need to bond some wood inside the hull or use a step drill to make the hole. Here’s the deal. Get a tapered furniture leg like you should have aboard anyway to pound into a broken off T-hull or hole to keep you from sinking... From the outside of the boat pound the furniture leg into the T-hull hole pretty hard. Then take a small hand saw and cut off the leg flush with the outside of the hull. Now you have a perfectly filled hole you can drill into with your hole saw....and you don’t even have to be super accurate and find the exact center. I usually just eyeball it—-plenty close enough and only takes a few minutes.

[Rotten Ricky]

Not all plastics are the same as cheap PVC which should never be used below the water line. Nylon and Marelon are far tougher alternatives if you do not want to use bronze or stainless, and they do not corrode. If this is a wooden hull, be sure to seal the wood very well before installing the through hull!

When installing the through-hull, apply the sealing compound like 4200 and only crank up the nut finger tight. Next morning, after the sealant is solid rubber, tighten up the through-hull properly. You should see a slight bulging of the rubber sealant around the edge of the mushroom head where it has been compressed slightly. This ensures that it has not only been chemically sealed, but mechanically sealed as well. It will never leak.

Another suggestion: Sometimes a little foresight can save a calamity. Instead of having a simple in-line sequence of the through-hull, followed by the valve, then barbed adapter and then the rubber hose which leads to the strainer, I suggest installing a T after the valve. In this new position, the hose now runs parallel to the hull because the barbed hose adapter is installed on the base of the T. This leaves a straight line between the through-hull, valve and the other side of the T, into which you install a plug. Why so?

This ensures that should you have any blockage from weed, or a plastic bag occur, you can remove the plug and stick a wire or long screwdriver down and right through the valve and through-hull and push the blockage away. You will get a bit of water gushing in, most of which you can stop with your hand, but it should be a minimal amount if you are quick. But at least the problem is solved. You could even do this to remove some molluscs.

Last time that I did this to clear a plastic bag, I shipped about 2 cups of water and it took about 30 seconds till it was plugged again. And all this costs is the price of a T and a plug.

One more thing while I am on a tear - try to route your incoming raw water hose so that you do not have to remove it in order to replace the belt on your engine. Unbelievably, this problem is often the case. Often this adaptation just means adding one or two inexpensive fittings, like 90-degree elbows, to the raw water pump so that the hose can now lead back close the block and then around to the strainer. Use nylon ties to hold it in place. You do not want to have to fight to remove a stubborn and old, well-adhered hose and deal with water etc if all you must do is replace your belt in an emergency!

Cheers, RR.