Water ingress and ventalation requirements

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Water ingress and ventalation requirements

Postby relay_guy » Tue Aug 04, 2015 7:23 pm

Greetings,
This is two-fold topic. #1, I get a small amount, 5-10 Gal on a 6hr cruise, of water ingress while underway. At he dock, she's dry. I assume that the pressure of the bow wave may be forcing water through the seams, but I dont know. I've checked the usual suspects, through hulls and shaft glands. Nothing to see, completely dry. Question, is this normal? I've had this phenomenon in both GB's that I've owned. If not normal, where would the most likely entry be?

#2. I've long considered adding a forced-air ventilation system to the tight areas below the decks. As mentioned, I do get some water down there underway. The boat is completely sheltered from rain, so thats not a problem Would such a ventilation system be worth the trouble?
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Postby Bob Lowe » Wed Aug 05, 2015 7:28 am

Typically, the most frequent points of significant water intrusion while underway, that is less or non-existent when not running, is shaft(s), rudder posts, and open seams (on woodies), particularly in the forward hull. Other potential sources would be raw water systems for engine(s), genset, refrigeration & A/C, and washdown systems.

I like to use Polyseamseal to seal the open seams as it tools easily with a wet finger, is white, completely paintable, a bit flexible and long lasting. We had to make this repair in Mexico when the seams opened up and we did it while in the water, from the dock and from a dinghy. Very effective, both functionally and aesthetically.

An easy way to ventilate the lower hull or bilge areas is to provide for air movement between all compartments from stem to stern and install some 6" muffin fans in the stern area, perhaps venting through the existing transom vents, and let those run when shorepower or genset ACV is available, either automatic or via a switch. The muffin fans can be either 102 VAC or 12 VDC. They are quiet and long lasting as well as inexpensive. And yes, it is worthwhile, at least IMHO. :)
Good luck,
Bob Lowe
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Postby Stretch Head » Wed Aug 05, 2015 8:56 am

About 12 or more years ago my boat was doing the same. I found it was hull seams near the bow as Bob mentioned. I also used the same Polyseamseal as Bob and that material is still holding. The thing I found on my boat was from above the seams looked fine, it was the underside that took on water. I laid on my dock finger to find the leaks.

Good Luck!
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Postby relay_guy » Wed Aug 05, 2015 10:30 am

Thanks so much! So, if I placed the muffin fans in the lazertette near the transom vents it would provide enough air movement to ventilate the entire lower hull area? The bulkheads would seem to be an impediment to the air flow.
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Postby Bob Lowe » Wed Aug 05, 2015 11:43 am

As I suggested, you should provide for air movement between all compartments. There may already be sufficient or you may have to cut some openings. Up higher would be best. The freer the air movement is the better.

I would also provide for the muffin fans to vent directly overboard via the transom vents or up onto the aft deck. You may have to provide a dorade type box to separate any exterior water and have it drain back outside while providing some protection to the muffin fans.

In the systems I have installed, there really was not much of a water problem. :)
Good luck,

Bob Lowe
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Postby Tom Overs » Wed Aug 05, 2015 5:37 pm

I may not be understanding this post correctly but,..... the engine compartment already has a fan installed to remove heat after running and that could provide any ventilation required (if any)

Now ventilating the Lazerette is something I think would be useful and as there is already vents fitted a small 12 volt fan would move air through it if fitted at one side.

Personally I don't like the idea of cutting holes in the bulkheads to provide extra air movement. I've always considered the lumber holes as a weak point if you start to take on water, cutting large holes in bulkheads seems callous in my opinion.

As I stated I may not be understanding this post correctly. :?: :?:

Tom.
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Born to cruise...........once forced to work!
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Postby Bob Lowe » Wed Aug 05, 2015 6:02 pm

I'm sure we all understand the concept of watertight bulkheads and compartments and their purpose of keeping water intrusion from spreading into other compartments in the event of a significant breach of the hull integrity. This is a common feature on ships and large yachts.

GBs and other similar small vessels are not designed with watertight compartments or watertight bulkheads. Heck, on your GB32, Tom, the floorboards will float away in the forward stateroom if the forward bilge fills up with water and there are plenty of other spaces against the hull for the water to pass and fill the cabin as well.

The limber holes will be the least of one's problem with a serious breach in the hull. The water already has plenty of ways to pass bulkheads. :(
Good luck,

Bob Lowe
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Postby Tom Overs » Thu Aug 06, 2015 11:56 am

Bob,
Floorboards floating in the forward cabin was how I found Little Ship, the sad thing was she was out of the water at the time :roll:

In the event of being holed ( heaven forbid) I want as much time as possible before LS goes under, I spent ages blocking off as much as possible only leaving the lumber holes.

As for ventilation..... This summer has been so bad I haven't even been able to leave the Lazerette open on a sunny day. Not to worry another couple of months and she'll be back undercover and drying out.
:x

Tom. :P
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Postby relay_guy » Thu Aug 06, 2015 1:39 pm

I really appreciate the comments on this subject as more than one shipwright I've talked to in my 20 yrs of wood boat ownership have suggested ventilating the boat. I'm like Tom and are hesitant to cut holes in he bulkheads, but the bulkheads in my 42 are mostly walls that separate the cabins. The only areas that would allow air circulation are below the cabin sole.

I think I'll ventilate the forepeak and lazarette separately. I can exhaust air from the fore into the engine room and use the main blower to vent it outside. I can use a new bilge blower to rout the air under the forward bulkhead. I can put two muffin fans near the lazarette vents and exhaust outside. I will design an electrical circuit that uses a cycle timing relay to provide automatic control. Should work.

I'll be out of the water in September to take care of the rotten transom and will inspect and repair the leaks that are probably around the stem are where the water gets in underway.

Pat
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Postby Oliver » Mon Sep 14, 2015 6:45 am

Where do you buy the muffin fans?
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Postby Bob Lowe » Mon Sep 14, 2015 7:12 am

Most computer shops should have a selection or try Amazon.
http://www.amazon.com/s/ref=nb_sb_ss_c_ ... Caps%2C229
Good luck,

Bob Lowe
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Re: Water ingress and ventalation requirements

Postby schono » Tue Oct 09, 2018 11:02 am

Revisiting this old thread, I've been having exactly the same problem described in the original post. I have a '68 GB 32 woodie and all indication point to water coming through seems while underway. However, I'd like to put it out the community to dig a little deeper and understand how that might have happened.

I acquired the boat just over a year ago, in May 2017. The PO indicated the bilge had been bone dry and had gone to detailed measures to make sure even small amounts of water did not get into the bilge: things like a plastic container under the shaft seal and a plastic under the water heater 'blow off' valve. However, just about a year ago, after having the boat only a few months, I first noticed water in the forward bilge after cruising for a few hours. I haven't determined if it has been enough trigger the bilge pump, but often it is high enough that when I operate the bilge pump manually it pumps water for a short while (<1 min) before sucking air.

Here are few potentially precipitating events:

1) The boat was moved from salt water to fresh water. She had been in the same covered slip in Des Moines, WA since at least 1973. We moved her to a covered moorage on Lake Union in Seattle.
2) A soft grounding while underway. Not too long before I first noticed water, I had strayed into on of the only shallow areas on Lake Washington, near Andrews Bay. The keep slid across the mud bottom until I could turn as I turned her toward the deeper water away from shore. This could be a likely culprit, but a haul out revealed no damage (see below)
3) Limited use. She's seen regular, but limited use, particularly at cruising speed over the last year: <100 hours. It has been hypothesized the planks above the water line could be a bit dry.

We hauled her out earlier this year and had the bottom repainted. Before the painting, I had a well recommended wooden boatwright (Mark Lerdahl, in Ballard) pull a half-dozen screws (they were all good), removed an unused thru hull (forward, formerly for raw water to the marine toilet), and recaulk seems along the middle-forward portion of the keel that had some black sealer in them. Other than that, there were not any planks that were noticeably separated. I was hoping the recaulking along the keel would stop the problem, but I've continued to get water in the forward bilge after sustaining cruising speed for a period of time.

What are your thoughts, GB community?

Thanks,
Scott
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Re: Water ingress and ventalation requirements

Postby bpbyrne » Tue Oct 09, 2018 5:27 pm

At the risk of contributing to this thread resurrection,is the polyseamseal mentioned the locktite stuff or something else? Is it any good on damp or wet seams?
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Re: Water ingress and ventalation requirements

Postby gsanchez » Thu Oct 11, 2018 10:09 am

bpbyrne wrote:
> At the risk of contributing to this thread resurrection,is the polyseamseal
> mentioned the locktite stuff or something else?

Yes
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Re: Water ingress and ventalation requirements

Postby gsanchez » Thu Oct 11, 2018 10:49 am

Scott, if the water only comes in while the boat is moving, then I would guess the issue is water coming in through the seams of the above-water planks at the bow.

This happens to to my boat, particularly at the beginning of the season after a long period of no use. In the course of the season it stops. I assume that by using the boat these above-water planks become wet enough for the wood to expand and close the seams.

I used Polyseamseal on these seams and have not seen any gaps between the planks. But I will check more carefully as Stretch Head suggests in his earlier post.

If water comes in even when the boat is stopped, then the problem would be below the water. One candidate for this that has been little discussed in this forum is a bad stopwater. I had a small but persistent bow leak that was eliminated when I replaced the stopwater in my boat last year.
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