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

[Bigjim]

When I pulled the boat out this year I noticed my engine intake had no strainer. It was also plastic and only protruded about a half inch through the hull. I checked the through-hull and seacock and they both measured 1 1/4 in.

So I ordered a 1 1/4 inch bronze through-hull and seacock and they arrived today. But when I measured the through-hull and the seacock they are 1 1/2 inches. What's going on? Are the sizes based on Inner diameter instead of outer diameter? And why doesn't it mention ID or OD in the product descriptions?

Should I send them back and get the smaller through-hull or just drill a bigger hole for the one I received? Would the larger diameter put too much strain on my water pump?

[Oceansailor]

Originally Posted by Bigjim

When I pulled the boat out this year I noticed my engine intake had no strainer. It was also plastic and only protruded about a half inch through the hull. I checked the through-hull and seacock and they both measured 1 1/4 in.



So I ordered a 1 1/4 inch bronze through-hull and seacock and they arrived today. But when I measured the through-hull and the seacock they are 1 1/2 inches. What's going on? Are the sizes based on Inner diameter instead of outer diameter? And why doesn't it mention ID or OD in the product descriptions?



Should I send them back and get the smaller through-hull or just drill a bigger hole for the one I received? Would the larger diameter put too much strain on my water pump?

Normally the Size reflects the OD.

[HopCar]

Pipe sizes will drive you crazy until you get used to them.

If you measured the OD of the thru-hull and got 1-1/4”, you probably have a 1” thru-hull. The actual measurement of 1” pipe is 1.315 or about 1-5/16” the ID will be close to 1”.

If the new thru-hull measures 1.66” OD, you received a 1-1/4” thru-hull.

[Bigjim]

Originally Posted by HopCar

Pipe sizes will drive you crazy until you get used to them.

If you measured the OD of the thru-hull and got 1-1/4”, you probably have a 1” thru-hull. The actual measurement of 1” pipe is 1.315 or about 1-5/16” the ID will be close to 1”.

If the new thru-hull measures 1.66” OD, you received a 1-1/4” thru-hull.

The ID of the through-hull is definitely 1" or very close. The ones I bought are marked 1 1/4" and the ID is 1 1/4" The outer diameter is about 1/2 more.

The secondary question is whether I use the ones I ordered or send them back and get the size I currently have installed on the boat?

[Tillsbury]

It's certainly not going to do any harm at all to have a bigger water intake. The only potential gotcha will be enlarging the hole, which is not the simplest thing in the world to do. On the other hand, if you're determined to add an external strainer to your engine thru-hull then it would do no harm to have it a little larger than the original 1"...

[a64pilot]

Originally Posted by Tillsbury

It's certainly not going to do any harm at all to have a bigger water intake. The only potential gotcha will be enlarging the hole, which is not the simplest thing in the world to do. On the other hand, if you're determined to add an external strainer to your engine thru-hull then it would do no harm to have it a little larger than the original 1"...

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.

However if it were me, I’d send it back and get the right size.
I have external strainers, they are the kind that attach to the hull and not the thru hull and can be opened from the outside, but I Sail in safe warm water.
If I were in cold or unsafe to dive in water I would not have an external strainer or if I were bound and determined to, I’d adhere it to the hull with 5200 only, so that it could be knocked off from the inside if needed by a broom stick or similar.
I ought to remove mine as they serve no purpose.

With an internal strainer that you can clean, you don’t need an external one that you can’t clean without diving the boat.

Of course if your a sailboat do not get the scoop style strainers, I wouldn’t on a power boat either though as you never know if you will be motoring on one or be towed

[Bigjim]

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.

However if it were me, I’d send it back and get the right size.
I have external strainers, they are the kind that attach to the hull and not the thru hull and can be opened from the outside, but I Sail in safe warm water.
If I were in cold or unsafe to dive in water I would not have an external strainer or if I were bound and determined to, I’d adhere it to the hull with 5200 only, so that it could be knocked off from the inside if needed by a broom stick or similar.
I ought to remove mine as they serve no purpose.

With an internal strainer that you can clean, you don’t need an external one that you can’t clean without diving the boat.

Of course if your a sailboat do not get the scoop style strainers, I wouldn’t on a power boat either though as you never know if you will be motoring on one or be towed

The internal strainer will work for small things, but if you motor through sea weed you could suck up some junk that could plug up the external hole. Then you are back in the same situation. Except now your seacock could be jammed too. If you can't close the seacock you're in big trouble. Most of the sailboats in my area have the strainers on the intakes. We have lots of sea weed in our harbor.

[Bigjim]

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

[Ambler]

Plastic is the biggest concern getting in to your cooling system strainer.
I have fitted a bronze strainer cowling over the 1"1/4 intake that I remove via 6 x 3/16" threaded countersunk bolts which are inserted into shallow tapped holes in my very thick solid grp hull. This strainer has a rounded leading edge and grills aft. It has kept the plastic out so far.

My through hull is 1" 1/4 and a plastic reducer is fitted to a 1" barb. The hose then goes to a strainer in the engine room.
I usually find a little crab ( only one time there wasn't) in the outer strainer that keeps it all clean. He can't get out through the grill because he has grown fat on the nutrients.
I would increase your hole rather than send it back. You can use a half round file or dremmel with a sander barrel.
Sorry just have an internal photo

[CarlF]

If you do get an external strainer be sure there's a way to remove it to clean barnacles out from behind it. Some strainers are part of the thru-hull and you have to try to clean them by inserting bits of coat hanger through the narrow openings in the grill. Using a long screwdriver from inside the boat will only clean the small part of the strainer directly below the hole.

[Cadence]

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.

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

[TrentePieds]

BigJim:

Size specs for any gizmo through which fluid has to flow is normally given as "ID" (Inside Diameter). Thus a 1 1/4" hose will not fit on a 1 1/4" spigot because the material thickness of the spigot walls, as well as the "bore" (the "hole size" or ID) of the spigot, will have to be accommodated within the bore of the hose.

If you don't already have one, get a measuring instrument called a "Vernier Caliper". They are cheap, and they are designed to measure (among many other things) both OD (Outside Diameter) and the ID of tubes, spigots rods and all sorts of other bits'n'pieces. If you get excited about it, right down to an accuracy of 1/1,000 part of an inch (a "thou") in common parlance. They also measure the Depth of holes.

Well worth the 30 bux it will cost to put one in your tool kit. When you have one, you never gain get caught with yer knickers down because you have been guessing at dimensions, rather than measuring them so you KNOW them :-)

All the best

TrentePieds

[Cadence]

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

[Niall leslie]

For what it's worth........

Tube is measured by OD, pipe is measured by ID. Different proportional standards for inside and outside measurements exist when comparing imperial and metric standard sizes. Tube is typically available in many wall thicknesses per each OD while pipe is only normally available in one wall thickness for each size ID.

The basic reason for all of this is that pipe is mainly used for liquid or gaseous transport while tubing is more commonly used for structural purposes as well.

If carefully selected, tubing can be also threaded using standard tapered pipe thread tools although commonly the threads for tubing are not tapered. If directly externally threaded through hulls do not use a tapered thread and are measured in the same way as pipe, i.e. ID in most of the World. Most ball valves available today are internally threaded and sized as per pipe standards. There may still be some sea cocks available with a tapered thread on the inboard end and a non tapered thread on the outboard end for the through hull as per some in the past. ( If it can be made to be complicated it will be!! )

The comments regarding seaweed are very valid and the holes or slots in an outside hull strainer should point aft for best performance with debris in the water.

Cheers,
Niall.

[Niall leslie]

Further - companies such as Groco make bronze adaptors which have an NPT male thread at the top for a ball valve and a female straight thread at the bottom for the through hull to avoid the common thread mis-match issue.
Cheers,
Niall.