Abandoning a Thru Hull

[skipperdude]

I have a number of plugged or capped thru hulls 3 to be exact. Plus a couple of transducers. Way to many holes and things hanging off my hull.
*I plan on hauling next spring. While she is on the hard I plan on doing something about these protuberances and divots. I am thinking about installing a sea chest therefore I shall not need them*
*Any thoughts?

 

[RickB]

Removing the unused xdcrs is probably worthwhile but what is to be gained by adding a sea chest?

 

[koliver]

what is to be gained by adding a sea chest?

a good place to store your sea boots and gold dubloons.

 

[Codger2]

I'm a big fan of sea chests! Sorry.....er.. I was thinking of something else.

 

[Woodsong]

Intersting thread as my boat is currently sitting out of the water getting some fiberglass work done. What all would be involved in removing abandoned thru hulls? I have a few as well that are not necessary and it would indeed be nice to eleminate them all together.

 

[markpierce]

I'm a bit slow;*what is the relationship of*hull openings*and chests?*

 

[FF]

The easiest way to plug an old hole is with a plug of GRP the same thickness as the hull.

An area will then be ground back inside and outside and glassed in after the plug is epoxied in.

The glass covering should be epoxy resin too.

A sea cheat is a great idea in a steel boat where the structure of the chest (a 12 to 18 inch pipe welded in) will match the hull.

As there is no shut off for the chest it must be strong .

In GRP a square box is easier to lay up and install, but the drag from a big hole may be higher than from std sea cocks bolted in and their thru hulls.

 

[jleonard]

I removed and glassed up several (5) *thru hulls in my boat the first winter I had it. FF even donated a nice piece of GRP for me as I was installing a new engine raw water intake

. Thanks again FF.

Lots of grinding around the old hole, to make up part of the thickness with a plug will help, and several layers of fiberglass mat each larger than the previous to make up the hull thickness. Inside and outside.
3 or 4 layers of gelcoat applied to the outside with a brush then bottom paint over that.

*

 

[Peter B]

RickB wrote:

Removing the unused xdcrs is probably worthwhile but what is to be gained by adding a sea chest?

True.* Skipperdude, I can't see the point of exchanging several quite small holes thru the hull, which can be effectively closed off if not used, with one humoungous hole which cannot.

*

 

[FF]

I can't see the point of exchanging several quite small holes thru the hull, which can be effectively closed off if not used, with one humoungous hole which cannot.



The humongus hole is less likely to plug up with plastic refuse underway , or jelly fish at night on the noisemaker or air cond circuit.

 

[jleonard]

FF wrote:
The humongus hole is less likely to plug up with plastic refuse underway , or jelly fish at night on the noisemaker or air cond circuit.

What I have done which has proven very successful (but not foolproof) is go up a couple of sizes when I put in a new thru hull. Not only does this help prevent underwater clogging it also allows for a larger capacity in the strainer inside the boat. I went from 1 inch to 1 1/2 inch for the engine (FL 120) and from 1/2 inch to 1 inch for the genset.* My genset has not clogged up with jellies or sweed since I upgraded size. (knock on teak)


*

 

[Larry M]

On our last boat we had 2-1.5"*thru hulls that went to strainers then each to a manifold with 3-3/4 ball valves.* One was for the water maker, salt water tap in the sink and generator.* The other was for the head, refrigeration and pressure salt water wash down.* It worked great and we only had 2 holes*vs 6.

We did find that*because we had*bigger thru hulls it just meant we were able to suck in bigger pieces of weed and debris.* We usually cleaned the screens every one to two weeks based on usage.

We have been*told that there some things you can take off a manifold or seas chest and some you shouldn't.* AC and water cooled refrigeration the "experts"*say*should be on there own thru hull.

Does any one know how much water*can come in via a wide open 1.5" hole in the bottom of you boat?

Larry/Lena
Hobo KK42
La Paz, BCS, MX

 

[Nomad Willy]

I have an old through hull that makes me nervous. It's in our hold and I need to be very careful to keep things from coming adrift and slamming sideways into the top of the through hull. Through hulls are/can be a very dangerous thing. But the plug needs to be more secure to be sure it's as secure as the old through hull. Corrosion of an old TH is very dangerous too. BUT if they are recent and installed properly, and big heavy things can't slam into them through hull are in my opinion very safe * * ...when the're closed.

 

[RickB]

Larry M wrote:
Does any one know how much water*can come in via a wide open 1.5" hole in the bottom of you boat?

If the hole is in a U-boat it depends on depth.

If the hole is inna you boat it depends onna deptha too.

gpm = 5.67 X d squared X square root of H

d = diameter of hole in inches
H = depth of hole in inches below water surface



Your 1.5 inch hole 3 feet underwater will flow about 76 gallons per minute at the start ... and*more as the boat sinks lower and lower until it stops flowing altogether.*

 

[Larry M]

RickB wrote:


Your 1.5 inch hole 3 feet underwater will flow about 76 gallons per minute at the start ... and*more as the boat sinks lower and lower until it stops flowing altogether.*

RickB:* Thanks.**That's a lot of water.* I'd better be able to find the hole real fast.**

I just looked at the flow curves for the pumps we have.* With the head, turns in the hose*and voltage drop*it doesn't look like our 2-3,700 GPH pumps will be able keep up with it.*

How much pump capacity should boats have?

Larry/Lena
Hobo KK42
La Paz, BCS, MX

 

[RickB]

Larry M wrote:
I just looked at the flow curves for the pumps we have.* With the head, turns in the hose*and voltage drop*it doesn't look like our 2-3,700 GPH pumps will be able keep up with it.*

How much pump capacity should boats have?

It looks like you should be OK, after all you are going to stuff something in the hole either from inside or out aren't you?

You can also put a Y valve in the engine SW inlet so that the engine can be used as an emergency bilge pump. Either that or install a clutched engine driven bilge pump.

*

 

[skipperdude]

Larry M wrote



*

*With the head, turns in the hose*and voltage drop*it doesn't look like our 2-3,700 GPH pumps will be able keep up with it.*

*I believe that the 3'700 GPH is rated at the discharge. At the pump. Not at the end of the hose.

I have a 400 gph with a 1/2' hose. Setting below my 4,000 main bilge pump.

The discharge for the main is I believe 1" or about a quart of water to flush back into the bilge.* The little pump has only about a cup of water in the 1/2" hose. Also my alarm is on the big pump I have never heard it go off KNOCK on Teak.

SD*

*

 

[Larry M]

Skipperdude:* Your right on the rating of the pumps.* The manufacturer rates them at 3,700 GPH*at the pump, with 0 head and at 13.6 VDC.**I figure with all the variables they might be pumping 2,200 GPH.* If they pump more, all the better.*

Larry/Lena
Hobo KK42
La Paz, BCS, MX*

 

[FF]

ON our 90/90 we use a 2 inch clutched Jabsco, and 2 inch pipe to the 3 compartments .

Claimed 120GPM , but we have only used it as a deck or anchor wash with a 1 1/2 seacock.

It sure DOES fill a dink really fast , or hose a wavemaker even if the smaller seacock is a restriction.

 

[skipperdude]

One thru hull that leaked

 

[rwidman]

Back on topic, I remember reading from an expert that removing a thru hull and repairing the hole is a lot more difficult than it would seem. Just filling the hole with fiberglass (or any substance) does not provide the same strength as the original fiberglass. To properly repair the hole, the area would have to be ground out and tapered to quite a large area, then filled in with fiberglass and finally gelcoat or paint.

It seems, the most practical repair is to keep the thru-hull in place and cap it off on the inside of the hull with a properly sealed threaded bronze cap.

It made sense to me reading it.

 

[Carey]

AllFor what it's worth, I removed a two inch thru hull eight years ago that led to a keel cooler. At the advice of the fellow installing my new engine, we did as a couple of you mentioned, and ground a taper into the hull that extended six inches out on all sides, both inside and out. This took us down to only about a half inch thick hole and about an inch of new glass depth in the middle. I check these patches from the inside any time I am in the engine room. I also look it over when hauled out. In all this time I have seen no sign of any movement, separation, etc. I believe, know what I do about fiberglass that it's as strong as the original.

 

[jleonard]

"Back on topic, I remember reading from an expert that removing a thru hull and repairing the hole is a lot more difficult than it would seem. Just filling the hole with fiberglass (or any substance) does not provide the same strength as the original fiberglass. To properly repair the hole, the area would have to be ground out and tapered to quite a large area, then filled in with fiberglass and finally gelcoat or paint."

That is precisely how I have filled all my thru hulls over the years and on different boats. I only use plugs at times to make up some of the space. I always overlap the "patches"
I would maintain that my repairs are sound.

 

[FF]

"Just filling the hole with fiberglass (or any substance) does not provide the same strength as the original fiberglass."

Don't run aground so the weight of the boat rests on the removed thru hull, if you are un-shure of your GRP ability.

Most repairs will have a single layer of glass on the outside (minimum) and about 1/4 inch thickness over a reasonable area on the inside.No problem unless point loaded.

 

[Larry M]

I was taught, when repairing fiber glass*to feather out 6 times the hole diameter for* making minor non structural repairs.* If you have a 1" hole you feather*out to 6".* You then do your layup*with the large patches first going to smaller.* Do not lay*up to many layers at once, 5 or so maximum*at one time.* You can*get an exothermic reaction that can weaken the catalyst.* There's a little more to it than this but it's not hard just dusty and time consuming.