Building a Sea Chest
 

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.

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.

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.

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'?

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'

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")

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

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.

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

PVA will be best for a new impatient to wax on wax off first timer
 

Your finish will be fine for a sea chest with pva. Alot of water is all you need for gun clean up. I also use water to remove my parts. from a mold. A wooden wedge to open a void enough to get water into the finished part will float it out of there and unstick the PVA back into a liquid. Lots of water for PVA clean up. No acetone or chemicals . Just helping a little to blue herons advice for a first timer.

What are the dimensions of the box? The smaller the part the less layers needed to keep it strong. This does not look like a very big project and I would not invest in a cup gun unless you are planning on doing lots more fiberglass work in the future. You should be able to brush on the gel coat if you do it carefully. I would do 2 layers of 1.5 oz matt and 2 layers 1708 and be done with it. I don't know why you would need to core such a small box? Coreing the bottom may provide a flatter surface for your plumbing?.... but I don't think it is necessary. someone help me here......

strick

Thanks for the info guys. I was going to core the bottom so I could run screws into the bottom to hold the pumps down.

the box will be about 21" wide flange-flange with the bottom of the box being aprox 17 3/4" the box will be aprox 10" wide flange-flange.

What is the difference between pva and wax? I have read of people using both and I have read of people using one or the other. Is one better than the other?

Hey Blue Heron I assume since you are thinning the gel coat you are using a tip around the 1.5 size? Have you had any luck spraying unthinned gel coat out of a larger tip gravity gun like 2.3 size? I have a few other mold projects I would like to tackle if I can get this one to come out right so the money on the gun wouldn't be a loss but if a $30 gun works as good as the $120 cup gun I would rather save the extra cash.

I plan on ordering my supplies from us composites seems like they have good prices. I am going to use vinylester for the layup if that matters.

strick is right. If your box isn't any bigger than that, you don't need to core it. strick has more experience than me on gelcoat application and layup. I've never been able to brush gelcoat without streaks showing up in the finished part, so I spray it. I would go with his layup recommendation too.

PVA is Polyvinyl Alcohol. It's basically a water soluble plastic. You spray it on your mold and it forms a film that looks like green saran wrap. Here's a link to a better description:

http://www.bottompaintstore.com/part...t-p-10321.html

They carry it at US Composites.

Dave

http://www.harborfreight.com/air-too...gun-66103.html

Has anyone used the above gun for spraying unthinned gel coat? It comes with a 3/16" tip which is what the cup gun uses for gel coat.

You are gonna want to wax and buff the mold several times and then spray it several times with PVA This is the best way to assure that the part does not stick to the mold.

I have not used the gun that you posted in the link but it looks like a good set up. I do have a cup gun for spraying gel coat and they are a little tricky to use. Because the cup is mounted horizontally on the gun the gun must be pointed up and the trigger pressed before you lower the gun or material will drip out the tip and make a mess. They let out a LOT of material. The gun that you posted looks much like a conventional spray gun and should be easier to use.

Your biggest challenge in this project will be a nice flat surface to mount your plumbing to so it will seal nice and even....in hind sight coreing it may not be a bad idea. I like Core Cell but on such a small project properly sealed plywood might be more economical.

strick

Strick, you have me thinking about the mounting surface now. The two raw water supply thru hulls and the pickup for the washdown pump will primarily be sealed on the finished surface (inside the chest). So I think those would be ok.

I am however concerned about the seacocks which will be sealed on the outside of the box. From looking at the unfinished side of other parts produced in a mold it seems like it would seal fine after the application of some 5200?

Thanks to everyone for the tips.

Mold is almost ready to go. My glass supplies should have been shipped from US composites today and I will probably begin glassing next wednesday or so.

If anything looks out of place or anyone has any tips let me know this is my first go at this type project.

Your mold doesn't have any taper. You will have to destroy the mold to free it from your part. Male molds that are intended to be re-used always taper from the opening to the inside. In other words, the closed end is smaller than the open end so it will slide out easily once you break the bond with the new part. I'm not saying it won't work, just that you need to think about how you're going to get the mold out without damaging your part.

Second thing is to make sure you seal your MDF with something to make it waterproof before you go any further. PVA is water based, and the MDF will soak up the water and the PVA won't want to dry. It will also probably raise the grain and make the surface rough.

I use clear lacquer on my molds, but I use masonite as the mold material, and that's smoother than MDF. Strick uses Duratech primer. I'm sure there are other coatings that would work, but Duratech is proven for MDF mold surfaces.

Your work looks good, though. Nice tight joints and good fillets and outside corner radius.

Dave

Dave thanks for the advice.

I was going to wax it with partall #2 before applying the pva do you think this would seal it up ok or should I paint it?

I have read about people making the mold smaller on the top. How much smaller should it be? Is it pretty much a guarantee that the part is not going to come off w/o tearing up the mold? If so thats ok but I would like to be able to keep it.

I was thinking I would drill several small holes in the sides of the mold and then fill them with wax then when I get the part ready to take off I will drill a tapered hole into the bottom of the mold that I can put my blow gun in and use a little air pressure to break it free.

Listen to Dave on this one. I made the same mistake on my first big fiberglass project. In the end I spent 3 hours hammer & chiseling the part out of the mold, while destroying the mold in the process while being EXTRA careful to protect my part....Taper is a must! My final part worked out okay, but my mold was trashed. Getting that "plug" out was a total P.I.T.A.!! I would say a 1/2" taper on 6" would be the minimum I would use. Say about a 1" setback for every 12" of vertical wall. Dave "Blue Heron" has more experience on that and may weigh in with his thoughts on minimum taper.

2 degrees is standard minimum draft angle. A small part like that might blow off. I found Honey Wax works well on that material. I did some tests and PVA was the least effective on MDF. Since it is already made I would give it a try what the hell. Stuff is easy to bust out, just add water! Just do your layup then drill a hole in the top to accept your air blower tip. Be sure to only drill thru the glass and not the plug. Then tap with a rubber mallet.

Well I decided to put a couple coats of polyeurethane to try and seal it up. We will see how it goes. Ringleader over on classic mako seems to have good success just waxing the mdf.

I am interested in removing these parts. How much force is usually required to separate the mold from the part?

After thinking about it I believe my plan of attack will be to drill a hole in the bottom of the mold through the mdf that will allow the air to get into the mold which will have holes drilled in it to allow the air to get in between the outside of the mold and the part.

Then I am going to thread a quick connect into the hole and hook up an air hose into it. Starting at 75 psi I will work the wedge around the flange and see how it goes. If she doesn't pop at 75 I will increase @ 25 psi increments.

If it becomes obvious that the part won't pop I will just unscrew the sheet of mdf from the mold and take it apart from the inside.

Thanks to everyone who has offered their opinions and advice.

Hope everyone has a Merry Christmas

Mike

I would not worry too much about saving that male one off mdf mold as it will likely warp or break before you ever use it again (mdf loves to absorb water)...plus it is not tapered like Dave already mentioned. They are cheap and easy to make anyways..... If you want a super smooth surface then you should coat it something before you wax....the wax alone will leave some streaks in your part...I dont know that it really matters anyways....how smooth your surface is....I was thinking it may have been easier to make a female one off mold but then your smooth surface would be on the out side. It would have been easier to free the part....be careful with compressed air and molds! If you did not seal/join the area where the base connects to the box it may leak air....then start a hacking away!

strick

Mold has 4 coats of partal #2 and three coats of #10 going to begin laying glass this morning we will see how it goes

Good luck, keep us posted...

If you plan on spraying gelcoat, I would thin it at least a little. It will spray a LOT better regardless of the gun. I have tried a variety of guns and have settled on an old school siphon style from Home Cheapo.

Popped the part at about 430 this morning had to break up the mdf wasn't too much trouble. Final laminate was 1.5oz mat/1708/1708/708/1708/1.5oz mat. Part came out pretty good. Most of the flange will be trimmed back.

Congratulations. Looks good. And with 4 layers of 1708, I don't think you need to worry about strength.

Dave

Looks good

Working on fairing the outside now. Knocked down the putty I spread over the outside and just went over it with some thickened resin.

Being able to make my own custom parts is going to be addictive. I already have a list of projects I want to do.

I have been working on fairing the outside for the last two days.

I am about to start drilling and cutting on the box for the plumbing pumps etc.

Does anyone have any experience overdrilling holes then filling with epoxy and tapping them for machine screws?

I am thinking of mounting my pumps this way.

I know exactly what you mean. It is very cool to be able to cut up a little cloth, mix up some goo to stick it all together and have a useful part you designed yourself.


Over drilling and filling with epoxy is used for wood cored laminates to isolate the screw hole from the wood. You don't need to do it with a solid laminate.

Glass laminate isn't ideal for drill and tap for machine screw threads but it can be done. Just make sure you goop things up real well with 5200. And you might want to back it up with a nut on the outside.

Dave

Got done trimming up the flange and put a radius on the corners. Also snapped a picture with the pumps just sitting in the box.

The wires will exit the rear and be sealed by blue sea cable grommets.

I am going to try the method Dave mentioned for fastening the pumps to the floor of the box.

After doing some reading on west system's website I was thinking of using thickened epoxy to seal everything up. Thought this might bond everything together well but would also be paintable so I could fillet the amount that squeezed out and make it look like there was no joint.

You might want to bed that in something more pliable and less permanent than cabosil thickened resin. Its going to be a prototype. You never know if you might need to make some changes, and thickened resin is brittle and will crack over time if there is any flexing.

Part looks good. Nothing more rewarding than an idea go from your mind to your hands.

Well I had my first set back this afternoon. Tried to make the lid for the box myself out of some 1/2" acrylic that has been in the garage for a while. Couldn't get it right. The cuts and the radius were both jacked up. I am going to go by the glass shop tomorrow morning and get them to make one for me. Thinking I may get two just to carry one on the boat in the event the lid ever cracked it wouldn't cut a trip short.

Ordered some 316ss machine screws to hold the pumps and the lid down. I ended up tapping the floor of the box and will hold the pumps down in there with 316 8/32 screws.

For the lid I am going to tap the flange and run 1" 10/24 screws it. I am thinking I will use around 24 screws in the top. 8 on top and bottom and four on each side. I am going to draw it out in the morning.

I tapped a piece of the flange (the flange is solid laminate aprox 3/8") that I trimmed off and tapped it and ran a screw through it. then I put the piece on the floor and put a foot on either side of the screw and tried to pull it out with a pair of channel locks. I couldn't pull it out even after putting about a 1" bow in the 18" piece so I think it will be fine with that many screws in it. I am planning on putting some silicone or something to keep them from vibrating loose. Maybe loc tight? Any comments or suggestions?

I need to order some sheet gasket to cut my gasket. I was thinking of using 1/8 or 1/16 epdm rubber. There are several options and I don't know much about the different choices. The two that I recognized were silicone and epdm. Any suggestions on these types of materials?

Nothing major going on in the last couple days just made a couple pieces to epoxy to the box that will screw to the hull to hold it in place. Also removed the rest of the pumps from the bilge and spent the day sanding the bilge yesterday. Got most of it knocked out.

Regrettably I will be out of town this weekend and unable to work on the boat. Will be back on Sunday and try to finish up the sanding and get a few holes filled with thickened epoxy. I am going to law down some awlgrip snow white in the bilge before I install the chest. I would like to get everything prepped so I can paint next weekend. We will see how it goes.

The chest and bilge are painted and I have the chest partially assembled. I hope to put everything back in the bilge and install the sea chest this weekend.

I am wondering what to use for sealing the many threaded connections when plumbing the chest. In two areas I have to orient the fittings a certain way so they may not be dogged down as tight as possible. I am looking for a compound that will be strong enough to keep a tight seal.

I have asked a few folks and got different opinions from pipe dope teflon tape marine sealant etc. I was thinking of using 4200 so it would be strong enough to hold everything together but I would still have the ability to disassemble everything if need be.

Any ideas on what would be the best product for this application?

I will post a few pictures this weekend. I have been bad about remembering to take pictures as I go along.

If it involves keeping your boat a float then I would use 4200 or 5200. Air mar recommends using 5200 to seal their threaded thru hull transducers.

strick