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Old 12-29-2013, 09:58 AM   #1
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I want to build a swim platform

I have a 48 foot Californian. 15'2" beam. I have a fairly narrow 2 foot swim platform. I am entertaining the idea of building a larger one of 4 foot wide. I have found a custom builder that wants 4200.00 to build one. How doable for the DIY'er? I'm fairly handy with tools and have the time. Now, wood core or divinycell? I want to build it stout. at least 600 pound capacity or better.

Any thoughts?
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Old 12-29-2013, 10:14 AM   #2
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If you're willing to work in fiberglass you can do it yourself. Quick answer to your question - do not use wood core! Closed dell PVC is best.

1. Make a full size template.
2. Make a flat table bigger than template and cover with shiny mica
3. Fabricate a flange that matches the edge of template of appropriate depth (6"?) surface with your shiny mica.
4. Wax no less than 6 times. No more than two times per day.
5. Brush/spray on gel coat 18 mills thick.
6. Laminate as necessary.
7. Insert core into wet mat or appropriate cement. Weigh down or vacuum bag.
8. Laminate on top of core.
9. Remove and trim.
10. Paint/glue on non skid.

In the way of the SS brackets you may wish to replace the core with solid glass ( during lamination).

Use 3m 5200 to bed when thru bolting to transom.
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Old 12-29-2013, 11:22 AM   #3
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Quote:
Originally Posted by knotheadcharters View Post
I have a 48 foot Californian. 15'2" beam. I have a fairly narrow 2 foot swim platform. I am entertaining the idea of building a larger one of 4 foot wide. I have found a custom builder that wants 4200.00 to build one. How doable for the DIY'er? I'm fairly handy with tools and have the time. Now, wood core or divinycell? I want to build it stout. at least 600 pound capacity or better.

Any thoughts?

doubling the width may present a few challenges, first off the brackets to handle the load vs. the moment arm related to the depth available on the transom to spread the load. also 4' may be a bit wide for the size of boat. keep in mind that at 60 sq. ft you can put a lot of load on the platform and the thing better be able to support at least 1000 lbs. if you really need that kind of depth to the platform you may need to look into a tank that is basically a hull extension.

Good Luck,
HOLLYWOOD
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Old 12-29-2013, 12:10 PM   #4
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Ahoy knothead

Seems you are looking to have a fixed-in-place Swim Step. I may build a new, larger SS for our Tolly. Iím impressed with design of Markís Coot SS. Its retracting ability interests me. For our boat it appears I would need to have the starboard portion remain fixed in position to keep the boarding ladder in position. From that area to port I can visualize a 3í 6Ē deep hydraulically operated platform with modified swim ladder. The construction of Markís SS also interests me. It appears to me relatively light weight in regard to its metal frame and planked surface. Iím not exactly rushing into things... but I do have my radar on for improved, considerably larger, yet retractable swim step alteration.

Thanks for this thread. Othersí swim step build-out input may get really interesting.

Happy Boating Daze! - Art
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Old 12-29-2013, 12:33 PM   #5
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there is a very extensive older threat on this if you search it
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Old 12-29-2013, 12:48 PM   #6
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Here are a couple good threads from recent past to start with. Dwhatty made a beautiful PlasTeak replacement last winter.

Alternative Swim Platform Materials

Swimgrid re-do
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Old 12-29-2013, 04:47 PM   #7
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Quote:
Originally Posted by hollywood8118 View Post
doubling the width may present a few challenges, first off the brackets to handle the load vs. the moment arm related to the depth available on the transom to spread the load. also 4' may be a bit wide for the size of boat. keep in mind that at 60 sq. ft you can put a lot of load on the platform and the thing better be able to support at least 1000 lbs. if you really need that kind of depth to the platform you may need to look into a tank that is basically a hull extension.

Good Luck,
HOLLYWOOD
Hear, hear. Not only static load, but the force of someone standing on it, jumping on it, lifting dinghies, occasionally bumping the dock, and multiple people. To double sounds a little unstable. (the platform not the owner)
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Old 12-29-2013, 04:50 PM   #8
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Check out Butler Marine, Duryea, PA. Seems you can have one made for a lot less. Might be worth checking out. I have a lot of work done by them

http://www.butlermarine.com/transom_platforms.shtml
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Old 12-29-2013, 05:33 PM   #9
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A heavy following sea at displacement speeds can allow the overtaking wave to ride up over the platform and potentially up and over the stern. Not a likely scenario under normal operating conditions, but something to be well aware of under those circumstances. I am in favor of retractable (or swiveling) platforms with good through drainage, that will be the route I take when I get to that project.
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Old 12-29-2013, 05:52 PM   #10
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I added a foot to mine as it was only two feet long. I removed the old one and the brackets. I then went to the local exotic wood supplier and had them mill me some teak 2 inchs wide to match the old platform. starting on the inside (stern side) I added the new material. Next I purchased some stainless flat bar and built new heavier brackets. Looks like the original just wider. Have fun.
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Old 12-29-2013, 05:58 PM   #11
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Take a look in Sailorman.com, I saw many used swim platforms to sell there.
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Old 12-29-2013, 06:15 PM   #12
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Quote:
Originally Posted by hollywood8118 View Post
doubling the width may present a few challenges, first off the brackets to handle the load vs. the moment arm related to the depth available on the transom to spread the load. also 4' may be a bit wide for the size of boat. keep in mind that at 60 sq. ft you can put a lot of load on the platform and the thing better be able to support at least 1000 lbs. if you really need that kind of depth to the platform you may need to look into a tank that is basically a hull extension.

Good Luck,
HOLLYWOOD

I agree. Our platform, added by a PO, is 29" off the transom. The original was slotted teak and not as wide. When we are at anchor or on a mooring, the wake from a passing vessel will shake Hobo as the wave compresses under the platform. Under way, the seas have never been an issue. Maybe if the platform was perforated, the loading wouldn't be as big an issue? 4' is getting pretty big but then again, properly designed, you would have enough room for a couple of chairs.
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Old 12-29-2013, 06:57 PM   #13
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Quote:
Originally Posted by Larry M View Post
I agree. Our platform, added by a PO, is 29" off the transom. The original was slotted teak and not as wide. When we are at anchor or on a mooring, the wake from a passing vessel will shake Hobo as the wave compresses under the platform. Under way, the seas have never been an issue. Maybe if the platform was perforated, the loading wouldn't be as big an issue? 4' is getting pretty big but then again, properly designed, you would have enough room for a couple of chairs.
Larry,
great picture!
it illustrates a couple possible issues.. on A KK such as yours there is not enough transom depth to get adequate support from the underside (most desirable) , also the above platform supports can be a trip hazard and are at times damaged when the stern swings wide (not a big issue on the KK as the platform is narrow in comparison to the beam. Also, below platform supports are mostly in compression under load (unless a wave is pushing up on them)... where the above platform support is in tension ad relies heavier on the hardware.
On the Krogen there is no other option and it is the best solution.

A vented platform really helps lessen the loading when waves push up under the platform.

HOLLYWOOD
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Old 12-29-2013, 07:19 PM   #14
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Quote:
Originally Posted by Larry M View Post
I agree. Our platform, added by a PO, is 29" off the transom. The original was slotted teak and not as wide. When we are at anchor or on a mooring, the wake from a passing vessel will shake Hobo as the wave compresses under the platform. Under way, the seas have never been an issue. Maybe if the platform was perforated, the loading wouldn't be as big an issue? 4' is getting pretty big but then again, properly designed, you would have enough room for a couple of chairs.
I like your dink ropes pre-attached and ready. Very good idea!
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Old 12-29-2013, 11:06 PM   #15
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I also have a swim platform on my list of projects. The more I think about it, the more I'm leaning to the Coot type retractible design. I'd have to add squaring ribs on the stern out to about 11 ft. or so to make it look right, but it seems to me that it would be no more expensive to go that way, so why not. The addition of a substantial swim platform would greatly enhance our man-overboard plan, and being able to retract the platform would help with dinghy retrieval (davits) and dinghy crane access to the stern.
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Old 12-30-2013, 05:37 AM   #16
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I want to build it stout. at least 600 pound capacity or better.

A good sized wave or wake can easily be more than 600 lbs.
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Old 12-30-2013, 07:54 AM   #17
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Thanks for all the input guys. Doug as far as coming up over the stern. If I had a wave overtaking my stern which is 8 1/2 feet off the waterline, I have bigger problems. The platform itself is 15 inches off the water line at rest. Underway a lot more, most of my cruising is done in the ICW had aspirations of the Bahamas but that will be a long way off there's a lot to see in the US first so not real concerned with heavy following seas. If I do go that large (4 foot wide) it will be vented to alleviate some wave pressure.
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Old 12-30-2013, 08:01 AM   #18
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Quote:
Originally Posted by knotheadcharters View Post
Thanks for all the input guys. Doug as far as coming up over the stern. If I had a wave overtaking my stern which is 8 1/2 feet off the waterline, I have bigger problems. The platform itself is 15 inches off the water line at rest. Underway a lot more, most of my cruising is done in the ICW had aspirations of the Bahamas but that will be a long way off there's a lot to see in the US first so not real concerned with heavy following seas. If I do go that large (4 foot wide) it will be vented to alleviate some wave pressure.
Not sure if it would work or last or even be desirable....but....if I was worried about the size, some removable or lightly attached inserts would resolve the problem of not enough pressure relief/drainage for when you encounter dangerous weather/huge wakes unexpectedly.
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Old 12-30-2013, 08:14 AM   #19
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These pictures are from a Selene that are factory made. My understanding is they no longer offer this option.
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Old 12-30-2013, 08:23 AM   #20
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Here's a pictures of the underside. The platform was made with plywood then glassed. We had it off this year and it takes 2 people to manage because of it's weight. It will easily support 1000 lbs or more. The top is 11.5" off the water at rest.
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