Mainship 400 Swim Platform

Bay Retriever · May 11, 2022

Has anyone had their swim platform removed, repaired and reattached? I currently have my 2004 Mainship 400 on the hard for a paint job (above the waterline to the rub rails). I would like to know what to expect in attempting this project and what possible unintended consequences could arise. Besides sandblasting and repainting/resealing the metal frame, how difficult will it be for the yard crew to break the through-transom bolts and replace reseal them?

T MACDONNELL
Bay Retriever
2004 Mainship 400

boan400 · May 11, 2022

Yes, absolutely. With great certainty, moisture has penetrated into the bolts below the water level.
I dismantled the swim platform in 2015 and a lot of water had entered in the hull in my 400 from 2005. No water into the boat only some rust was visible from the inside.
There was no protection around the bolts, only balsa wood to the bolt. Very poor solution from the factory.

I dismantled all the screws in the stern and replaced the hole swim platform with a larger one built in Gprs. I don’t have any bolts below the waterline, which I am very happy about.
Bolts through the stern below the waterline are a big risk on the Mainship hull.

Check water penetration and rust on the inside which bolt holes leaks in water. Note that water can leak into the hull without it being visible on the inside.

If that is the case I proposes to dismantle the swim platform and all bolts, remove all wet balsa and fill up with epoxy and drill new holes.

Dougcole · May 13, 2022

boan400 said:
Yes, absolutely. With great certainty, moisture has penetrated into the bolts below the water level.
I dismantled the swim platform in 2015 and a lot of water had entered in the hull in my 400 from 2005. No water into the boat only some rust was visible from the inside.
There was no protection around the bolts, only balsa wood to the bolt. Very poor solution from the factory.

I dismantled all the screws in the stern and replaced the hole swim platform with a larger one built in Gprs. I don’t have any bolts below the waterline, which I am very happy about.
Bolts through the stern below the waterline are a big risk on the Mainship hull.

Check water penetration and rust on the inside which bolt holes leaks in water. Note that water can leak into the hull without it being visible on the inside.

If that is the case I proposes to dismantle the swim platform and all bolts, remove all wet balsa and fill up with epoxy and drill new holes.

Makes sense and is darn scary. Please let us know what you find TMac.

Doug

Comodave · May 13, 2022

I would absolutely do the reefing out the balsa around the bolts, fill with thickened epoxy and redrill even if you don’t see any leaks. Your transom core may be getting wet as we write this. Much easier and less costly to do it before the water travels too far from the holes.

boan400 · May 13, 2022

Mainship made a big misstake to not reinforce with epoxi around the bults. Simple and inexpensive at the production stage. The sandwich construction is not good at stand by high pressure on small spots, a microscopic pumping effect occurs around the bults.
But listen at Comodave he put it well.
My boat had been in the water half the year for ten years at the time I discovered wet balsam around several bolts, which is why I recommend everyone to do as Comodave described asap.
It may be possible to do from inside, on the hard. Depending on how extensive the leakage is.

Comodave · May 13, 2022

How accessible is the transom from the inside on a 400? On my Formula you have to be about 5’ and 100 pounds, neither of which am I…

boan400 · May 14, 2022

Comodave!
I,m sorry not following you about the space in your Formula but in the 400 it`s lot of space to investigate the stern from the inside.
If I missunderstand you or you wan’t some pic’s, let me know.
Boan

Comodave · May 14, 2022

No, there isn’t any room in my Formula at the transom, a real PITA. I was just hoping you would have more room than I do. Maybe I said it poorly…

Bay Retriever · Jun 21, 2022

boan400 said:
Yes, absolutely. With great certainty, moisture has penetrated into the bolts below the water level.
I dismantled the swim platform in 2015 and a lot of water had entered in the hull in my 400 from 2005. No water into the boat only some rust was visible from the inside.
There was no protection around the bolts, only balsa wood to the bolt. Very poor solution from the factory.

I dismantled all the screws in the stern and replaced the hole swim platform with a larger one built in Gprs. I don’t have any bolts below the waterline, which I am very happy about.
Bolts through the stern below the waterline are a big risk on the Mainship hull.

Check water penetration and rust on the inside which bolt holes leaks in water. Note that water can leak into the hull without it being visible on the inside.

If that is the case I proposes to dismantle the swim platform and all bolts, remove all wet balsa and fill up with epoxy and drill new holes.

The swim platform has finally been removed. The yard left the four support brackets/arms on the boat so I could see that three of the four brackets are cracked where the bolts enter the transom. below the water line. Now I need to find 4 replacement support arms. Anyone know where to find replacement support arms? My boat is a 2004 Mainship 400. Here are some pics.

T MACDONNELL

Comodave · Jun 22, 2022

Looks like custom metal working to me.

Mainship 400 Swim Platform

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