Building a Sea Chest

[mbmcdermott18]

Gentlemen, new member here with a couple of questions. I am in the process of planning a sea chest. I am going to make a male mold to accomplish this. This will be my first major fiberglass project and I have a few questions.

I have read that once the mold has been waxed properly (I plan on using partall#2) the mold does not have enough surface tension to brush the gelcoat on. I am trying to determine if I need to spend the extra cash on the cup gun.

On the layup I was thinking starting and ending with a layer of 1.5oz mat with four layers of 1708 45/45 biax. How are these products to work with? Should they lay down decently once wet out? Any suggestions as to how I should cut the glass to conform correctly or how much overlap there should be?

Thanks in advance for any advice you can give. I am going to atach an image of the sea chest in case someone is unsure as to what I am talking about.

[77SceptreOB]

Whats all that for? What does it accomplish? Sprainer for raw water cooled engine(s)? and bait/live wells? How do you clean it out? I'm confused, looks like a lot of work and valves, etc.

[mbmcdermott18]

Basically it keeps the livewell pumps which are bilge pumps in this application from air locking. when the pump is mounted directly on top of the through hull like mine are now the smallest amount of air causes the impeller to cavitate. With the sea chest the pumps are always submerged in water preventing an air lock.

The plexi lid is removable if you need to clean it out but I have gemlux high speed pickup which should prevent any grass from getting into the chest. The plumbing is rather involved but I think it will be worth it. Right now my pumps air lock anytime I back down hard or I come off plane which is a big pita.

This design was pioneered by Fred Herman from what I understand and is commonplace on the south florida sailfish circuit where they carry hundreds of gallons of live bait.

Many builders such as conch, contender, invincible, weaver, sea vee and others use the sea chest to supply raw water.

[workinpr0gress]

Hey mbmcdermott18 I like the idea of seachest, you see more and more on smaller boats. Are you planning to glass it integrated into the hull, or are you going to plumb to it? Do you have a 23'?

[heynow2203]

So you only have one pick up feeding this if I'm not mistaking? Also is there standing water in the chest or is it piping tied together? I have always hated the air locking in the system and would like to do this on my 23'

[mbmcdermott18]

I don't have a seacraft. I hope I am not stepping on anyone's toes posting a non seacraft project but after reading this forum and classic mako I felt like these were the only two places I could find the information I needed without a bunch of crap that you run into on the bigger forums. For some reason my registration won't go through over at classic mako.

This sea chest will be mounted in the bilge and plumbed. The water will be supplied by two 1" thru hulls with high speed pickups. Larger sportfish's sometimes have a setup similar to this built into the hull and it is open on the bottom with a large grate over it.

Do ya'll think the laminate will be strong enough with the four layers of 1708 and and two layers of 1.5oz mat? My calculations show the final thickness will be about just over a quarter inch plus gelcoat (0.266")

[Blue_Heron]

Originally Posted by mbmcdermott18

Do ya'll think the laminate will be strong enough with the four layers of 1708 and and two layers of 1.5oz mat? My calculations show the final thickness will be about just over a quarter inch plus gelcoat (0.266")

If it's not any bigger than the one in the picture, 1/4" of laminate is overkill. You can get away with 1/8" if you make the high stress areas (where fasteners and seacocks mount) thicker. That assumes the tub will be well supported once it's installed.

I would core the area where the seacocks are going. That will stiffen it up and provide backing for fasteners.

Dave

[mbmcdermott18]

Blue Heron, Thanks for the advice. I had considered using a core material and still may on the bottom where the pumps will be screwed down. One reason I thought going with a thicker laminate all the way around is because the chest will have plumbing or screws on every side. Also the box will not be supported underneath. It will be resting over the keel and fastened to the hull on the sides with wings like the chest pictured below has.

[mbmcdermott18]

Can anyone who has made a part with a waxed mold tell me if I will be able to brush the gelcoat onto the mold or will I need to spray it? I have read mixed reports on this.

[Blue_Heron]

Originally Posted by mbmcdermott18

Can anyone who has made a part with a waxed mold tell me if I will be able to brush the gelcoat onto the mold or will I need to spray it? I have read mixed reports on this.

I've brushed gelcoat and I've sprayed it. I've gotten better results spraying it. If you have a compressor, spray is the way to go. I use a $16 gravity feed gun from Harbor Freight and thin the gelcoat 20% with acetone. Thin the gelcoat before you add the catalyst and use 2% catalyst based on the pre-thinned volume. Make sure you have at least 15 mils thickness of gelcoat.

For mold release, wax is good, PVA (Partall Film #10 if I remember right) is better for this application. PVA must be sprayed. I use the Harbor Freight touch up gun @ 60psi for PVA.
Dave