Aereation of double bottom hull

[Granitu]

Guys, as part of a routine full haul service I am doing on  my 14ft fregatina, i was chatting with a guy from a local boatbuilder and told me that it is advisable to have aeration holes for the double bottom (the space there is between the fake bottom and the real bottom).

He is of the opinion that it prevents the building up of osmosis (not my concern since i never leave the boat at sea but leave it in a garage). In one of these holes I will be fitting a through hull transducer using marine sicaflex (again, in his opinion sicaflex is better than epoxy resin especially if accidentally the bottom is hit or you need to remove it-however i do have no doubt that sicaflex is an excellent product and resists very well the marine environment).

he recommended that these areation ducts on the hulls during winsterising time are left open so that no moisture builds up. When i told him that in there there should be a vacuum he told me that it is virtually impossible in the humidity we have that no moisture builds up in the double bottom space since in principle raw fibre and some epoxy resin absorbs moisture enough to build up osmosis eventually. He did show me some of his boats and they are all rigged up in this manner and never fail him but cannot compare the material strenght to mine.

To be honest i am quite sceptical to drill 5 holes (12cm holes) at different places around the bottom part of the boat as i think i will weaken the face of the hull where i will fish, stand up and do other things.

What do you think guys? Am I foolishly worried? Is it really necessary?

[fisheye]

I know friends that have inspection holes cut into the double bottom that when on the hard they keep open for same reason you gave. It is very important that they are made watertight when at sea. 

[Granitu]

Thanks for the reply fish-eye,

the screw tap is available at caruana marine which has them available for some reason for sure. They have a tight o-ring.

In my opinion i will instruct to drill 2 holes (on opposite sides) only which should be enough to inspect the hull.

the boat i saw rigged up this manner was a tar-ratal boat.

I am still wary about it originally i was thinking of drilling the transducer in the single bottom part (where we fit the engines) but he immediately called it off because if some leak happens the hull would be exposed to sink - he was right on this one in my opinion

my concern is that five holes will weaken the fibre glass, but his reasoning is quite right to be honest

[fisheye]

I think that tar-ratal knows a thing or two about boat building. Maybe you should try to contact the company that build your boat and see their perspective as well, may be they advice you on whats the best way to go according to your boat model and specifications.

[Granitu]

silvercraft il fregatina - to be honest he was quite skeptical about the material thickness because there are 2 versions of the boat.

Tar ratal guy was quite informative even if the prospect that i am looking to build a 20-22feet boat he is intentional to offer me his service when I am still undecided what I will buy - I will need some sea trials and ideally inspect the boat hulls and fibre with a fellow marine surveyor and build on his opinion (he is one of my fishing buddies)

[shanook]

where did u drill the holes for the water intake of the engines in the double bottom or in the single bottom?
I think that the installation instructions tell you to keep the transducer away from the engine.
I think if you use sicaflex there is no problem of any leaks that is if you do things right. Drill the right size hole, tighten the nut properly and apply the right amount of sikaflex, clean the contact surfaces.
If you cut two holes, it should be enough for a 14ft boat. u can always cover the boat with a tarp (kabus or whatever you have as a cover) and place a dehumidifier inside to draw the moisture out for a few days. There are moisture absorbers (silica gels) on the market, a 8''x5'' (500gram) one is approx 16 Dollars.

[Granitu]

the guy who fitted the engine drilled in the single bottom part but i never had/have any problems and no signs of osmosis whatsoever. However i will ask for advice as the guy who fitted the engine nearly destroyed my engine because he did not design properly the exhaust system which i got fixed by bonnici stores instructions (in have a yanmar - it was drawing water in the exhaust valve)

I DO HIGHLY NOT RECOMMEND ANYONE TO INSTALL AN INBOARD ENGINE AT THE GUY RESIDING NEAR ST THOMAS BAY SLIPWAY. HE SHOULD PLAN THINGS BETTER.

Since the single bottom was already drilled, i presumed to put my transducer there. However i will leave the job to the professional and fit 2 holes opposite to each other for aeration purposes with one of them fitting the transducer. Till date i was using a clamp on system which worked but i want to free the transom from clamping.

I do have a humidyfire but i winsterise the boat properly so all I am doing is for precautionary purposes and i think a humidyfire procedure + these 2 holes will be enough since I am having no troubles till now.

The guy proposed to install the transducer a little far away from the engine for the vibrations reason too. Like he did it on his boat.

I will speak to Caruana marine on Wednesday and see his opinion (he sees a lot of people I presume he hears a lot of stories so he may have a reliable opinion on this) since i will buy the parts from him and Thursday get this job done. Will upload some photos when ready.

In the mean time i may ask you:
what water barrier paint you recommend
what anti-fouling paint you recommend

possibly even the procedure to follow

Another recommendation i got was to paint the water part with anti-fouling paint.

what paint to use to paint the inside of the boat? - even the procedures to follow

A normal hammerite paint is good to paint a trailer or 'qatran li jizbghu bih l qiegh tal karozzi' is better?

After i finish exams its time to work hard on new clients for my company and overhaul over the boat to get her ready for the fishing season... about time lol

thanks for the replies sorry for being over demanding I just want to do the job once and right

[shanook]

I would rather drill the single bottom rather than the double bottom. The double bottom should be left as water tight as possible. If there is a water leak u see it in the single bottom. if u have water in the double bottom than u sink without even knowing.

water barrier paint? what are u going to paint the boat or trailer??
antifouling paint for the boat or the transducer face?

No i do not recommend hammerite. hammerite is porous if not applied exactly right. I would go for a two pack epoxy pain for the trailer, make sure that the metal is clean from rust, and oil deposits.
For the inside of the boat there is Damboline by international marine paints (IMP).Its a very good paint. Actually I would paint the double bottom (should have been done before hand in my opinion).
For the outside of the boat if it has not been done yet then there are various water barriers that can be used and everyone has his favourite. I used mine by IMP. Its a lengthy process and must be done properly. Its the life or death of a boat.
regarding antifouling well is it a fast or rather slow boat. As thge speed affects the choice of antifouling. I usually drive in the 8/12 knots and i use self polishing or self leeching again by IMP. there are a lot and i know that the one by Wurth is good so is the one by Camilleri marine. I have used all of these and they did the job.
Antifouling for the transducer. DO NOT TOUCHT THE TRANSDUCER FACE WITH ANY TYPE OF SOLVENT BASED ANTIFOULING.  I never antifoul it, I use an oil based gel from Caruana marine. Ask him for this and tell him where u want to apply it. Sorry but it is at garage cannot tell u the make or name.

[Granitu]

shanook the boat has still the paint silvercraft did on their boats.

I am enquiring about the guy's suggestion and see if it is really needed.

first of i will not touch the transducer with any solvent paint i know it should not be messed up However i will instruct to follow your recommendation shanook. PM me the garage name if you can shanook

Secondly, the anti-fouling paint is still a question for me. I never leave my boat on an irmigg (i don't have one and not wishing for one) , i trail it to garage always. the idea behind the anti-fouling treatment is that any scratches will scratch the anti-fouling which they are quite resistant to sctarches. I have no vegitation concern

I don't have any double bottom holes yet - and the original post was intended to determine whether it is worth to do these holes in the face part for aeration.

Eventually i built the post up and answered all the relevant questions hehe..

so i don't know if it was painted with an anti water barrier treatment or not the inner bottom ( i cannot see it as there are no holes yet). what i know is that it is that the outer bottom was already painted by silvercraft and it is in such prime conditions that the wax treatment used for the 'forma' some of it is still there - bottom part. But it is not an antifouling paint and small sctaches have to be gel coat painted. I always kept the boat in prime conditions.

What I was adviced is to scrape with a sandpaper the bottom enough to let the antifouling grip and apply a water barrier and subsequently antifouling but I am presuming it is a more complex process

It is not something i need urgently to do, but it is advisable i think to inform myself better and develop a plan for action

I used the boat quite frequently but nothing ever happened and there is no osmosis but I believe prevention is better than cure and we can always learn

the inner paint has three layers of paint I know of, one white which is peeling off, one kind of grey undercoat not peeling and after a black coat not peeling on the fibre - but some of the first layer paint (white) is scraping now and i decided to restore a paint for a nice view and a protection film

I will follow your advices and speak to caruana marine for the products settting priorities (time concern) xi haga nirrangaw

thanks shanook for your feedback very helpful and kind of you.

The maintenance im planning on the boat will cost me the same value and more the value i bought the boat. But that's boating I guess

[Moonwalker]

I was told that if boat is not in the water for more than 24hrs there is no concers about osmosis so no outside painting is needed.

[Granitu]

i think so moonwalker but you never know.

Thanks for the information that's quite useful

[shanook]

dont bother with painting or antifouling if the boat is not constantly in the water. Antifouling drags the boat. If there are scratches then fill them up with proper filler and then apply a coat of two pack epoxy paint for the whole bottom. this is more than enough. its a tough paint and scratch resistant. Antifouling is not any good for scratches. it peels off very easily (its supposed to do that).

[Granitu]

thanks guys i will avoid this unnecessary expense than

[skip]

Granitu, if you want to do the aeration holes I advise you do not buy regular inspection screw hatches, but use Solas A type approved. The main one on the market is made by Whale-Henderson and is called a TCL-4

http://www.whalepumps.com/marine/product_list/10/67/

It's approved for use on life boats and when you are on the hard you can just remove the lids to achieve what you desire.

[Granitu]

would i find available in malta? ideally i have to have them available by thursday. Seem strudy for sure