Swim platform bracket mounting

[HotSpot]

Hi All

Inspired by some of the ongoing swim platform projects going on here, I decided to get in on the action too.

Building the platform is relatively straightforward, but I’m not certain on how to mount it.

I have some triangular brackets that would allow installation above the waterline. For the upper bolts, I’m planning to through-bolt with a backer plate. I see this as the most critical for strength since the weight on the bracket will pivot outward toward the top.

However, the bottom of the brackets are in question. My first inclination would be to through-bolt those as well. Unfortunately, the position of the bolts would enter through the transom in an area that is inaccessible without further opening/cutting of the deck.

One option would be to not through-bolt the very bottom, and instead just surface mount those.

Most of the usual force on the bottom portion of the bracket would be toward the transom. My concern is unusual forces, such as a wave coming from behind.

Do you guys think that through-bolting the top but surface mounting the bottom of the brackets would be adequate?

Thanks!

[Donmystic1]

I have a. Full set of stainless steel brackets that will fit a 28 or a 31.

$50 plus shipping

Don

Mystic, CT

860-460-3282
Text me you email for pictures of the brackets and how I mounted my platform

[HotSpot]

Thank you, Don, for the photos you sent via email.

I’m not sure if those would work, as the longer ones may be too long.


The ones I already have are 9” tall and extend out 17”. The cross member is like 20”.
The good thing about them is that the installation would be above the waterline.

[Tony Meola]

Hopefully one of the 25 guys with a swim platform will jump in and help you out.

[Carl]

Do not discount to force of wave action, could be many multiples of fat Uncle Sal jumping on the platform to pull two ton Tess out of the water as one of her swimmies deflated and her doughnut's getting wet.


Seriously...10' x 2' platform slamming down onto a wave makes for a hell of a lot of upward force.
Think anchoring with a large yacht passing behind you at a good clip.
Backing down is another great way to see how sturdy your brackets are attached.
Following sea...

They take alot of abuse...

docking...well, think this crowd should have that down...but holy mackerel have I seen some good hits taken by swim platforms.

[HotSpot]

You paint quite a picture, Carl!

I am actually jealous of Sal and Tess since it is going to snow here tomorrow.

Here's about where I'll be needing to cut. You guys recommend maybe something like a 2 to 3" hole saw down from the top? From there it wouldn't be visible when the panel is replaced. Then keep it open for access?

How large of a backing plate is necessary? The plates behind the outdrive bolts are only about 2x3" each, so I assume that may be a good size.


(All that dirty lookin dust is from the cork floor being sanded down)

Again, thanks to everyone for your opinions.

[Yannis]

Hotspot,

Do not underestimate the fact that when you accelerate your stern goes down. In that low stern position with respect to the water surface, you do not want the platform to plow the water, it has to be positioned high enough and be narrow enough to clear the V shaped sea water.

In the pic you show your holes should be above the thick hollow part. Why cut? Place your holes in the white rim, right below the green glass. The boat thickness there is double and I would just put a thick washer, no special backing plate.Consider that you do not necessarily need those L shaped outside supporting brackets with their predetermined holes.

What is the platform made out of? Does it have an outer SS frame?

[Yannis]

In these two pics you can see my inside and outside configuration.

https://imgur.com/a/Yqt0M88

[HotSpot]

Hotspot,

Do not underestimate the fact that when you accelerate your stern goes down. In that low stern position with respect to the water surface, you do not want the platform to plow the water, it has to be positioned high enough and be narrow enough to clear the V shaped sea water.

In the pic you show your holes should be above the thick hollow part. Why cut? Place your holes in the white rim, right below the green glass. The boat thickness there is double and I would just put a thick washer, no special backing plate.Consider that you do not necessarily need those L shaped outside supporting brackets with their predetermined holes.

What is the platform made out of? Does it have an outer SS frame?

Thanks for the pics, yannis

The platform will be wood, with no surround frame. However i’m contemplating a rub rail around the perimeter. The platform is still under design, pending the placement of the brackets.

This pic of ttownthomas’ prospective boat (hope he doesn't mind) has the best view I have seen on a 25 with outdrives, and I am planning to follow this general placement and layout of the platform and brackets. It sits pretty high due to the outdrives, so no worries about dragging on hole shots.



I just wish I could see how it was mounted on the inside.

It’s the placement of the bottom bolts of the brackets from the inside that I am curious about, since the bottom of the brackets that I have will be in that hollow spot if the platform is at the height that I like (similar to this pic). I could consider raising it even higher, but then it may be more of a diving platform. I may need a longer boarding ladder too.

[Yannis]

I think that the platform in your pic is perhaps too wide. I’ve never been on a 25, but it’s my impression that the platform’s extremities might be in the way of the inward wake created. Make sure it’s not, because this issue might become important when accelerating in a wavy sea.

The other point is the outside brackets. The issue here is how many and how low they reach. This guy has four, the two right and left ones seem to be at such a small angle I doubt their efficacy, or their contribution to the overall downward torque.
You could get rid of those two if you added one in the middle if it doesn't bother the engines turning, which doesn't seem it would. The major thing here is the angle. Your L shaped brackets may be too shallow. In other words, they don't seem reaching low enough to obtain a good stability. Of course I may be wrong as I cannot tell by the pic, but to me, at least the middle one should reach as low as possible, like it shows in my own pic. Otherwise, the stress on the top bolts will be more than you’d expect.
Mine are welded at the top, under the platform’s SS frame. You will also have some sort of frame where the wood will sit and be bolted on. Why not make so that you position by design your frame’s transversals right on top of where you will put your three brackets? Then you bolt the frame to the boat.

As for the ladder, you shouldn’t worry too much. It’s more important to place the platform at the right height, even if you might have to get a new ladder. Mine is on the side! I found it there and immediately thought it somehow strange for a ladder to be there. However it has a lot of positive points so after I tested it for a season I ....left it where it was! It is retractable and stows under the platform so it doesn't take up space on top.

Finally, I wish to add that here in the Med all boats have platforms. You will see add-on platforms, like in our older type boats, or, you will see platforms molded on the hull during construction, that extend structurally behind the transom. In both cases we cannot do without because this is the easiest, if not the only way, to get into the boat after a swim. And all boats in the Med are for swimming, very few are used for fishing. It’s also the area where most of us keep our tenders, so they are built sturdy to withstand the weight in rock ‘n roll conditions which is the norm.

PS: If you find that the level of the platform should be higher than where you suggested in previous posts, or shown in the pic of my boat, don’t let it bother you. You make the holes where they should be, only in this case, just because the transom thickness is lesser, you can spread the weight by widening your outside flanges so that the platform “sits” on a wider surface, and you add the corresponding backing plates on the inside. Consider also that the platform’s frame is bolted onto the transom in only two areas (right and left), all the while having three outside vertical supports, that’s why a frame is also a better solution structurally. Good luck.

[Preston Burrows]

Yannis,

For what it's worth the 'classic' B28 O.E.M. swim platforms were affixed by way of 3 sections of stainless steel tubing [1" diameter usually] which had flat tabs top and bottom......the top tabs were through bolted with backers behind the transom and the bottom tabs were lag screwed directly in to the stringers, two fasteners in each tab, top tabs attached to the platform and bottom tabs attached to the stringers.

The O.E.M. platforms had a flange on all four sides which aided fastening, there were also separate through bolts and backer plates behind the transom for the inboard side of the swim platform next to the transom.

I removed the backers for the 'inboard fasteners' and replaced with a 2" wide 1/4" strip of aluminum across the entire width of the platform, which served to stiffen the assembly and provide a 'non rottable' continuous backer [I installed a stud for Bonding and wired the aluminum strip to my Bonding system.]

As you and others have alluded the swim platform attracts a wave beating, the method above serves to provide sufficient give and take strength wise......

Lastly this reminds me of how my B28 sank during Hurricane Matthew in 2016.....my mid-ship breast lines failed / stretched to the point that the transom / swim platform was beaten against the aft dock pilings which sent the centre and starboard supports through / ripped them off the transom at the lower tab fastener position and the resultant 6" diameter holes sent the hull underwater.......perversely I did take solace, and Bertram pride, in the fact that my backyard engineered top aluminum backer held strong with no damage whatsoever...............

[Yannis]

Crap, you lost your boat? Damn, at least did you get anything from the insurance?

[Chanse]

This on my B26, 5 tabs next to hull under platform,3 brackets outer to lower platform, alum hand made.
I'm doing some things here you never would want to do in the salt.

[HotSpot]

Thanks everyone! I never expected such varied and contradicting advise!

Actually, really appreciate the feedback from everyone.

Here's where I am headed now...
1. I am going to make the platform about 6 inches more narrow than the transom where it will be mounted.

2. Originally,the platform was going to be about 22-23" deep, but now considering it to be more like 19", which is just a couple inches beyond the length of the brackets. My only concern is that the outdrives stick out about 22" from the transom. Maybe this would be dangerous for unfamiliar swimmers/jumpers. I recall a friend who banged up her backside pretty good on an outdrive when sliding off a platform (stub) of a boat she wasn't familiar with. Maybe at 22-23" this would still be a potential problem anyway with flailing body parts.

Chanse - yours looks rather narrow. About how deep is it? Any complaints from people who have been accidentally bumped off?

3. Considering to raise the platform a couple inches from the original height so that a the bottom bracket bolts can come through where Yannis had recommended at that double thick portion of glass. This will also remedy potential blockage of the bilge outlet. All brackets will be through-bolted, top and bottom. I'll consider some more robust backing solution for the upper mounts, as suggested by Preston. - Really sorry to hear about your boat being sunk.

Thanks again, all!

[Yannis]

Hotspot,

Fine.

Could you at least measure the exact position of your 3 brackets and the exact space between them and then go weld them together?
That way you would have created a small frame which you could through bolt onto the stern. On it you could then bolt the platform.
I my mind this provides for more lateral stability. You could even increase the depth, to 22' or even more, now that the platform rests on a unified frame.
A deeper platform, except for protecting accidentally falling-off swimmers, also protects your props from docks or pilings when mooring or when the wind picks-up while you're finishing off that last glass of wine away from the boat. The frame could take a beat like that better than the three individual brackets...

[Lars]

For inspiration, here’s a pic of the platform installation on my 25. You will need to position the brackets differently due to the outdrives, but I think the width and height of this one is pretty perfect. Too wide and it gets in the way when maneuvering; too narrow it gets silly. Too low and you will keep slapping it in the water; too high it gets precarious.

I will change the ladder to the under-mounted kind though.

[Yannis]

Good example.

A good frame and just two supports. And a good 25 or so cm inside EACH side. And a wonderful teak work...

Lars, for your info, I’ll be in the central Aegean from early June until late September... look up in google earth the island of Syros and more specifically the little port in the southwest called Finikas, as well as the island of Sifnos, and the port of Platys Yalos at the southeast. In those two ports I spend most of the time because we have family in those islands.

[Lars]

Thanks Yannis.

And hey, the Norwegian summer weather turns disappointing, I just may come knocking... Looks like a wonderful place.

[Chanse]

HotSpot, 18" never any problems, it has stood the test of time!

[HotSpot]

Wow, thanks again everyone.

Yannis, I like the idea of tying the ends of each bracket together for more support. Ideally, I'd do what Lars has with the complete surround frame, but time and budget prevent that. That platform looks so pretty.

Also great point about having the depth of the platform extend past the outdrives for protection from backing into things. I have an especially small amount of room from my slip to the pier behind me. If my neighbor ties up too far back, I have to get really close to the pier to make room for my bow to swing around . I may have bumped it once... The pier.

That is such a nice platform (and 25 in general), Lars. I went back and read your earlier posts, including the one about the lettering which has excellent pictures of the platform and the frame without the deck installed. This link has the pics of the frame in great detail in case anyone come across this thread who's looking to do the same. I wish I had found this a lot earlier, but we need to splash in a couple weeks and this project is a couple years past due. Another summer without the platform will not go well with the crew.
http://bertram31.com/newbb/viewtopic.php?f=2&t=13200

This is getting exciting. I'm going to start laying out the frame tonight. I'll make provisions for up to 5 different mounting points. One center, and two on each end. It will look a lot like Chanse's, but curved to follow the transom. I'll plan on using either 3 or 4 brackets, but may get crazy and bring on all if it's too flimsy with a bench test. Need to invite uncle Sal over for a go at it.

Thanks all!

[Yannis]

Hotspot,

Tie not only the loose far ends of the brackets, but also the corner ends near the stern.

Also do not rush things...if you have not enough time to make a platform to the correct specs, not only about the frame itself but also about the wooden surface, you can start this year with a 2,2 cm thick marine plywood cut to a shape, that will show THROUGH ITS USE whether its the right size or height...treat it with some flimsy varnish, stick a few antiskid tapes so its not slippery, have the kids paint on it their desired colors so they feel in the loop, and off you go. Next year you'll know exactly what you need (how high, how wide etc) and your crew will be happy this summer too. And you would have tested everything for the price of a piece of ply, I'd say in the $ 30 range. Best of ALL worlds.

[HotSpot]

Hotspot,

Tie not only the loose far ends of the brackets, but also the corner ends near the stern.

Also do not rush things...if you have not enough time to make a platform to the correct specs, not only about the frame itself but also about the wooden surface, you can start this year with a 2,2 cm thick marine plywood cut to a shape, that will show THROUGH ITS USE whether its the right size or height...treat it with some flimsy varnish, stick a few antiskid tapes so its not slippery, have the kids paint on it their desired colors so they feel in the loop, and off you go. Next year you'll know exactly what you need (how high, how wide etc) and your crew will be happy this summer too. And you would have tested everything for the price of a piece of ply, I'd say in the $ 30 range. Best of ALL worlds.

Yannis, If I tell my wife we will mount a piece of plywood to the boat for this season, I’ll hear no end of it.

However, If we call it an “engineering prototype”...

Anyway, that’s actually a great idea. I could easily pull the boat to swap decks later in the season if the first placement works out and I have time to complete the final design /build.

[Yannis]

Yea “engineering prototype, or Dick Bertrams’ first platform mock-up, you know! IT’ll work, Im sure!

[HotSpot]

Just wanted to post an update.

Construction of the platform is complete. Difficulty was in getting to the boat which is 5 hours away. Second difficulty is that I am a hack at woodworking. So, this is more of a carpentry experiment.

So, fist trip up to the boat, I was able to take a template of the transom curve using some scrap 1/2 plywood sheet. I used the washer in a pencil trick to trace the outline from a rough first cut. Took that back home and scribed to a 2x12 to make a form, making note of the measurements for the "bump out".

Since I didn't know if this would turn out, I started with some boards that I had leftover from a previous project. They were cut them into strips that were about 1 3/4 inches. Basically ripped the 1x4s in half. The boards are box store "mahogany" which is not mahogany. Although I'd prefer teak, it was easy to cut, very straight, cheap, and very accessible. It also was pre-planed and jointed, which is important since I don't own tools for that.

Left them at full length of about 8 feet, and screwed the ends of the first two boards to the form after gluing, screwing and clamping.



Figured that I would account for using any configuration of brackets, up to 5. plus a mounting surface for the under-mount ladder. I really wasn't sure how strong the platform would be once built, so I planed for the worst. In my mind this would just be a prototype anyway.



Finally got to the boat this weekend for a dry fit, and to cut out the bump. The measurements came out well, however I should have accounted for a little spring-back from the bowed boards. The ends at 44" from center came back about half an inch. Still follows the transom curve well, but could be better.

Decided to finish it with West System epoxy; 105 resin with 207 hardener, with a varnish top coat. This was my first time doing an epoxy finish coat, so I started on the underside as practice. Results were acceptable. Now that the end grain is sealed, a removable border surround will be screwed into the perimeter.




For the brackets...
I decided to go with all 5. When I mocked up 3 (two ends and one center, it seemed that there was enough strength on the platform, but was still worried about bracket strength. When I did 4, which was two on the ends, and two just outboard of each outdrive bracket, it was very solid. Then I figured why not just put in the last center one too.

This is taking a bit longer than I had hoped, but the fortunate thing is that since the water on Lake Michigan is so high, we are still on land while the marina is having height extensions welded to the finger piers. With any luck, this should be done just in time for the marina to open.

Sincere thanks to everyone who helped me out with this.

[Yannis]

Good, very good!
I still think 4, and certainly 5 brackets is an overkill.
Now, what this wood is or isn't, will show in the future. If you've done a good sealing work it should outlast...you!
Have fun.

[Tony Meola]

Platform looks great. That is a nice job.

[cariedl]

The platform looks great. I'm just now weighing in, but I have four brackets for mine, two very close to center that are the main support brackets and two L shaped brackets just outboard of the exhaust to eliminate any flex in the platform. Almost all of the structural weight are through bolted to the middle angle brackets, similar to the one in your previous post. The marina who mounted it used West System 5200 so there are no screws/bolts running through the top of the platform.

Good luck with the rest of the project, can't wait to see it on your 25.

[Chanse]

HotSpot. You Got Talent! Looks Great.
Sounds like your doing what I did for years...Chicago burbs to the County, Over & Over.

[HotSpot]

The plan finally came together last weekend.

Went up with one of my brothers and father under the guise of a quick fishing trip...

First thing in the morning, we got to work fitting the final outboard brackets with some backing plates. Since these are only are supported by 1/4 of woven fiberglass, we made backing plates about 5"x5". Once those were in, we screwed the platform down using lag screws and marine sealant from underneath the platform. If ever it appears that this is not holding we can drill through and use bolts, but I didn't like the aesthetic of having the carriage bolts come up through he top. (We did this for the under mount ladder). We could have recessed the bolts and used plugs, but I was on a time schedule. So, this will have to do for this season anyway.



I tested the ladder on the dry. It was good for my <200lb frame. My slightly more massive co-conspirators were reluctant to test it. But it seemed very solid. After this dry fitting, I decided that we will add two more segments which will add 2 inches in extension, but that will be done next year. For now we will leave it with the butcher block looking ends that are sealed up really well with an extra layer of epoxy.


We launched the boat and went for a quick sea trial. Any concerns about the prop wash or that wake surge thing that happens when throttle is suddenly cut were allayed. No issues except for some spray coming up. There is plenty of clearance. Although since it was a dead-calm day, we didn't really have a chance to see what happens when a nice wave comes over, but I think we should be good with all the drainage slots available.








By the time we had everything buttoned up at the new dock, and figured out our tie-up situation, there wasn't much time left in the day for fishing. However we did get a little time in for a cruise and were treated with a nice display from mother nature.... maybe a good omen for the season.


Thanks again to all who gave advise on this project. It has been a great learning experience. If anyone wants some assistance on something similar, please reach out. I have all the measurements and details on construction that I can share for any other 25 i/o who's looking to do the same.