PVC sea chest??

[ted655]

I need a sea chest around the stem of a thru hull transducer. The stem hole is 1 1/16". IF ever that transducer were to shear off, you'd sink in a New York minute! My solution is a 3" or 4" dia. piece of PVC pipe, sealed down to the hull, higher than the waterline. A pipe sea chest.
1. Any better idea? 2. Best way to attach pipe to hull. I'm assumeing fibrtglass cloth or tape & epoxy.
Thanks,

[Lancerbye]

Actually you wouldn't sink that fast and most boaters I know carry tapered wooden plugs for such an occasion. I did however do something similar to what you suggest on a commercial aluminum gilnetter. He wanted more speed so I was doing a streamlining and power upgrade. He had this big transducer sticking out of the bottom surrounded with a heavy guard. I took the whole thing off, cut a 3 in hole in the bottom of the boat and welded a 3 in aluminum pipe with a top plate. so he could have a recessed transducer. I know most people get a bit squimish about making holes in the bottom of boats.The only consideration I would worry about in what you are proposing is in the attachment of PVC pipe to fiberglass. For a more attachable solution get a piece of 3 in. fiberglass pipe and a cover piece. They will glass in place nicely (especially with a cold cure epoxy). PVC is difficult to properly attach to fiberglass. Nothing adheres to it well except pvc glue when attaching another pipe or fitting.

[ted655]

Thanks. I didn't know PVC was hard to glass. Where do I find fiberglass pipe?
I can't recess my transducer. It has to protrude and can't have a guard either. It's FLS (forward looking sonar) & projects a signal forward, along & ahead of the hull.
I wasn't going to open the sea chest to the water, just surround the stem in case of a crack or hole as a result of collision.

[PI Design]

Fibreglass pipe = broken windsurfer mast?

[ted655]

Thanks, BUT.... nobody windsurfs in Louisiana. Is a WS mast 4" dia.?

[PI Design]

Shows whjat I know - I assumed LA was Los Angeles!
The bottom of a WS mast might be 3", but I doubt 4".

[trawler builder]

hi , take your pvc pipe and wax it up really good ,then lay up the length of pipe you need and pull out the pipe and there ya go you will have your piece you need to glass to your boat

TB

[Lancerbye]

If you can't find fibre glass pipe in your area (usually available from fibreglass fabricating companies) you can easily make one yourself by using the PVC pipe as a female mold. Wax it up a bit if you want to remove it afterwards or leave it in place as an extra liner. Use Fibreglass mat and don't be cheap with the resin. About 3 layers of 2 oz. mat should do nicely. The PVC pipe makes a great mold.

[Lancerbye]

I guess great minds think alike LOL

[ted655]

Gotca. Thanks. Should I flange the bottom as I lay it up, where it will sit on the hull, or just glass around the joint with a fillet of thck epoxy?
Attachment TO the hull was why I asked here to begin with (not knowing PVC wasn't suitable).

[Lancerbye]

I would fit the pipe to the location with a fibreglass putty properly filleted at the joint and the glass the joint out about 1 .5 to 2 in up the pipe and the same away from the base. Your going to have to make a plug or cap for the top which will allow the wire to pass out of the top for service. there is very little pressure at that depth so a bead of silicon seal will help to seal the whole thing.

[ted655]

---"Your going to have to make a plug or cap for the top"----------
Not really. A sea chest is built so's the top is open, the edge is abpve waterline and no water enters the bilge. I saw one on a tug that had several different inlets in its walls, feeding water for other purposes. A cap is only needed to keep the dolphins from jumping in. In my case, it wouldn't even be open to the water. Just a "dam" around the hole the transducer stem needs. A "safety chest" in case the transducer should be damaged or destroyed.
3M 5200 is supposed to be some tough adhesive/sealent. I've never used it. Would IT be suitable to adhere the P VC to the hull? Might it be brittle? If the sea chest is not made fast to the hull and breaks also, then there was little point in even doing it. I'd like a method/material that becomes part of the hull. The fiberglass tube seems better.
Thanks,

[Lancerbye]

I remember seeing 3M 5200 used on boats but I can't remember what it was used for. I suffer from CRS desease (can't remember ****). I know of one very sticky adhesive that might work. I used it to attach stuff to fibre glass decks etc. as a base compound when attaching hardware to a deck etc. after when I wanted to remove the attached piece. after the screws or bolts were removed I had a heck of a time removing the fitting. This was Sikaflex http://www.sikaindustry.com/ipd-marine.htm (amazing stuff. Check it out.

[SamSam]

It seems like poly resin fiberglass sticks to pvc, but it can be peeled off. You could use the pvc as a mold and you don't really have to remove it, just glass the whole thing down, pvc, glass and all. Rough up the pvc, wipe it good with acetone, then laminate.
What's going to be a problem though, is if you ever have to work on the transducer to replace it or something, you'll probably have to remove your sea chest.
Maybe you could take the pvc and wax it and lay up a ring on one end a few inches high. Then you could laminate that ring to the hull so you'd end up with a flange on the hull that you could insert the pvc into, with caulking, and then screw through the flange to secure the pvc. If repairs had to be made, you would only have the flange to work around and not have to work down the length of the pipe (or cut it off). Sam

Better yet...
If they make a threaded pvc flange for 3-4" pvc, you could glass that down to the hull, glue a threaded pvc adapter on the pipe and then just screw it into the flange glassed to the hull.

[ted655]

Oh Sam Sam! Great idea, (why didn't I think of that). Nooooo, I would have glassed it all in & later had to destroy the whole enchalada just to remove the nut.
This whole forum is great for just the fact that a fresh set of eyes will see the obvious. Also..., links to products are very helpful.
Thanks all.