Swim Platform Slap

[DCDC]

I have been considering modifications to our swim platform to reduce slap. There is a current thread about hull slap noise for boats with forward cabins so I thought I’d ask about your experience with swim platforms.

Our platform is super functional, about 30”x 8’, aged teak with slots and stout. Primary use is in & out of our dinghy. It’s about 1” above the waterline, which is convenient, but slaps in the slightest swell or waves. Very noticeable in the aft cabin.

I would like to raise it, a considerable job, and want to get it right the first time. How high are yours and do you have problems with slap?

Thanks in advance.

 

[koliver]

I have been considering modifications to our swim platform to reduce slap. There is a current thread about hull slap noise for boats with forward cabins so I thought I’d ask about your experience with swim platforms.

Our platform is super functional, about 30”x 8’, aged teak with slots and stout. Primary use is in & out of our dinghy. It’s about 1” above the waterline, which is convenient, but slaps in the slightest swell or waves. Very noticeable in the aft cabin.

I would like to raise it, a considerable job, and want to get it right the first time. How high are yours and do you have problems with slap?

When I removed teh old supports, some (most?) of the bolts, though SS, had corroded down to less than 1/8 of original diameter. It was time, at 25 yrs or so.

Thanks in advance.

Unless you have no access to the inside surface of your transom, where the bolts will need to go, raising your platform to as much as 12" above the water shouldn't be a huge chore.
I extended my original platform from 20" to 33" (roughly). In the process I had to build new supports, and couldn't (wouldn't) use any of the original's mounting holes. As the lower part of the vertical of the supports are in compression, against the transom I purposely did not put a hole/bolt below the waterline. The balance of the holes you will be drilling in your transom are in tension or neutral, and with decent access, this is a 1/2 day job at most.

At 12" above the water I have never had slap. At the former height of 10" I had none.

When I removed the original supports, I found the bolts had mostly corroded down to 1/8 of original diameter. It was time, after 25 years.

 

[Jeff F]

I'd raise it to the level where your dinghy will not go under it. You don't want the stern of the dinghy getting caught underneath in waves. Guesstimate 10 -12 inches?

I had a similar platform at that height on my Mainship and got the occasional slap but usually there was other noise/motion at that point

 

[OldDan1943]

Dragging the swim platform through the water while underway is no benefit so why not raise it. Per the dingy sliding under it, put out a few fenders.
Your swim ladder and a low hand rail, on the swim platform, should settle anything else.

 

[BruceK]

The Integrity 386 and 426, and other models, incorporate the swimstep into the hull in a shallow extension which part sits permanently in the water. It has 2 approx 6" wide quite deep slots cut into it underwater. Result is lots of slap noise, even minor "bumping" from wave action striking transom when at anchor/moored when it occurs. Probably similar in a following sea.

I think it`s done to be selling a bigger boat, and extend waterline length.

 

[OldDan1943]

I think it`s done to be selling a bigger boat, and extend waterline length.

Bingo.
and it makes the dock master happy when he rents you a slip

 

[BruceK]

Bingo.
and it makes the dock master happy when he rents you a slip

Well, I told them, truthfully, it was the IG36 hull, minus the teak swimstep, plus the same depth of swimstep now incorporated into the hull. My dock fee, calculated on 36ft, did not change. I`d have accepted an extra 2ft a month charge but it never happened. However the slap does, but it`s tolerable.

 

[OldDan1943]

Well, I told them, truthfully, it was the IG36 hull, minus the teak swimstep, plus the same depth of swimstep now incorporated into the hull. My dock fee, calculated on 36ft, did not change. I`d have accepted an extra 2ft a month charge but it never happened. However the slap does, but it`s tolerable.

It is the documented length. My documented AT34 is the same as the AT36, including its swim platform.

 

[Simi 60]

Hinge it.

 

[rslifkin]

My platform is about 8 inches above the water and 20" long. No slap issues from the platform, but if we take a decent wake on the stern, it makes a pretty good slap against the transom, then a good splash as the water shoots up the transom through the platform slots against the transom. I've also never seen the platform hit the water underway any time I've looked.

 

[DCDC]

Thanks for all the valuable feedback.

 

[Steve1.0]

Quote: " The balance of the holes you will be drilling in your transom are in tension or neutral, and with decent access, this is a 1/2 day job at most."


Rather than removing the original mounting brackets, how about having a fabricator fashion a vertical extension, similar to a table, which bolts to the existing brackets, on which you remount your platform.