Building a swim platform

3

390x

Member
Mar 12, 2009
818
Moline, IL
Boat Info
1989 390 EC
Engines
454 Merc BWI
Well, because the factory platform was deficient in so many ways, I've started building a new one for the 390. It's roughly 140" wide by 44" deep. I'm building the deck out of two sheets of 1/2" plywood laminated together. I cut the slots in it for the factory teak inserts because i like them, and I'm going to be adding a hatch with the folding ladder under it, and a water-tight locker for a stern anchor and some ropes. I'm also adding a couple of pop-up cleats as well. It should take about 8-10 gallons of resin/hardener. I'm going to use 3 layers of resin/cloth, so it should be rock solid after that. Actually, with all the framing in place, it's rock solid right now. I'm hoping to start glassing next weekend. Let me know if the link to the pics doesn't work.

http://picasaweb.google.com/115874118884999438016/SwimPlatform#5691773948665774786
 
I love the project thanks for sharing with us...

One question though... what type of wood are you using for the core? Looks like regular lumber... keep up the nice work and keep us posted...
 
Marine Plywood for the deck...........which is exactly the same as what you buy at Lowes, it just (supposedly) has a different glue. The rest of the lumber is exactly what you'd buy at Lowes......If everything is done right, It'll never see water anyway. I'm giong to overbore all the holes for bolts, and anything that will get screwed to it, and refill the bores with kitty hair so no screws/bolts will be into wood, so the coring can't/won't get any water intrusion.
 
Now is this pressure treated stuff... or real marine plywood my local HW stores do not carry marine plywood... sorry for the 20 questions...
 
No, it's not treated. I don't know that the resin would stick to the pressure treated stuff. I got it from a local supplier. He had to order it for me. Actually, upon re-reading, the difference between marine ply and regular ply is that marine ply absolutely will have no voids in it, but regular ply might.
 
Impressive project and a great skill from you!

I’m just a little afraid the original slots could not be sufficient to relief all the possible pressure from waves under the platform.

The Swimplatforms.com I installed has one row of slots along the transom edge. They are really like little geysers!!!


DSC_0950.jpg
 
That will be a nice addition, just make sure the attachment points are sufficient to carry the weight of the SP and another 1,000 lbs minimum. It would suck to go through all of that work and have it rip off and sink your boat!
 
Pietro, I thought quite a bit about whether or not to put relief holes near the front like yours has, but when I look at a lot of other factory platforms, they don't have anything like that. My parent's Carver doesn't have any relief mechanism of any kind on it. I guess we'll see.

As far as the attachment points, I was planning on at least 1/4" aluminum plate on the outside, and possibly aluminum c-channel on the inside of the transom.
 
May I suggest adding an inside corner block behind the outside radius corners. If you were to ever back a corner into something, it will stress that corner immensely! Good luck!
 
Trying not to nit pick. It looks like a very good job. I realize this is a work in progress, so forgive me if this is something you plan to do, but had not yet. I would suggest putting fairly aggressive radiuses (radii?) on all edges. Fiberglass cloth, even when completely saturated, does not bend well. Having soft corners (1/2, or even 3/4" radius) will allow it to lay against the wood and prevent air bubbles. I would do this on both the exterior edges and interior corners. The interior corners you can use a compatible caulking and route the edges.

I'd also paint all of the end faces/edges with epoxy and allow that to cure as a first step.

Henry
 
Henry Boyd said:
.

I'd also paint all of the end faces/edges with epoxy and allow that to cure as a first step.

Henry
Click to expand...


Do you plan on using all epoxy to encapsulate the platform? or epoxy? I am not 100% but I think epoxy will stick to most anything but the polyester will not stick well to the epoxy if you use a bit of epoxy first on the end edges.

John
 
Loneranger said:
Do you plan on using all epoxy to encapsulate the platform? or epoxy? I am not 100% but I think epoxy will stick to most anything but the polyester will not stick well to the epoxy if you use a bit of epoxy first on the end edges.

John
Click to expand...


Good catch, I assumed he would be using epoxy only because that would be my preference. Without getting off course on a epoxy resin vs polyester resin discussion, the point that is important is to seal the open grain end edges first.

Henry
 
looks good so far but for what its worth I would have done things a bit different. I would not have used the 2 x lumber that you did. Would have been better to use the marine plywood (much better than pressure treated) and laminate it together to get the thickness you need. 2 x luumber is not that stable and can twist, warp or split to easily. I would also have used rabbet joints and a poly glue instead of nails and the liquid nail as it would provide more strength.
Also good call from another post on rounding over all the edges before appling cloth.
 
Looks great. Please keep us posted with more pics. My only concern would be weight, it even looks heavy. There is a guy here on CSR that made some fantastic inserts. Can anyone remember the thread?
 
Last edited:
Looks nice - Keep the pictures comming. The ply instead of the 2x stuff would have been a good idea but at this piont I would probably just finish it and it should be fine.

LK
 
I understand about the ply vs the two-by, but this is good dry lumber, so any twisting that was going to happen already did by now. I'm ahead of you on the radiusing of all the edges. I agree that most cloth won't make a very sharp edge. I just got done with the quarter round bit on the router doing all the edges, and where I couldn't hit with the router, I hit it with the belt sander. I used a poly glue laminating the decking together, and heavy duty PL on all edges for the dimensional lumber. As far as weight, It's not too heavy yet. I can easily lift an end with one arm, move a sawhorse, and set it down. I'm guessing maybe 175lbs at this point. It'll get a lot heavier with the resin and cloth. I'll be using polyester resin. The epoxy is nice, but I don't know, in this application, if it's worth the extra money. I've helped build a few of these, and the poly seems to be holding up well. I plan to do 1-2 coats on EVERYTHING with just resin before I get around to laying any cloth on it.

I added a couple more pics. The radius doesn't really show through that well without a closeup. I did a lot of sanding and rounding today, and made the cutouts for the teak grates square. Hoping to be glassing by next weekend, but all the places I'd considered ordering from are closed this week. It might be a stretch anyway. I still have to make my anchor locker, and the hatch for the ladder. Those are probably at least an evening a piece projects.

https://picasaweb.google.com/115874118884999438016/SwimPlatform#
 
Last edited:
With this design will you need to add the supports under it or will it support itself like the swimplatforms.com ones do?

LK
 
You must log in or register to reply here.

Forum statistics

Threads
113,143
Messages
1,427,186
Members
61,057
Latest member
DrBones!
Back
Top