Swim platform ideas for older Sea Ray

[tobnpr]

Here's this guy again.:smt043

If you've got something to say, say it...no need to be cryptic, what's your point|


I've not used Coosa. It's not cheap, but neither is replacing the swim platform in a few years. If you're going to consider it, PM our sponsor, Jim. He used it when restoring his Seacraft.

The problem with swim platforms is that there's constantly shifting stesses on the fasteners- eventually they can begin to "work", the sealant around the fasteners fails, and water gets into the core. If I were to build it with a plywood core, I'd overdrill the holes and fill with thickened epoxy, then re-drill for the fasteners as has been discussed here before.

Edited to add:

These are pictures of the results of the thermal expansion/contraction of Starboard/Seaboard. No, the fasteners were not overtightened at installation. Fortunately it splits cleanly, I'm going to glue the pieces back together and throw in a dummy screw head and drill for new fasteners nearby. This time I'm going to overdrill the holes...

 

[Danny Troy]

Is that Starboard, or Seaboard, and is it the better heavier Starboard? I know there are different types of Starboard, or other polymer sheet products made by King. After working with Starboard on a few projects I can't see it cracking as you show. It will bend, but not crack. And considering Starboards price, I wonder if it's more impervious to this cracking???

 

[Dasch Boat]

The access panel at the underside of my radar arch has cracked right across from screw hole to screw hole. I would like to remove it and glue it back together this spring. Please let me know what adhesive you wind up using, I've heard that these products don't accept most glues and sealants.

 

[shore]

If you've got something to say, say it...no need to be cryptic, what's your point|


I've not used Coosa. It's not cheap, but neither is replacing the swim platform in a few years. If you're going to consider it, PM our sponsor, Jim. He used it when restoring his Seacraft.

The problem with swim platforms is that there's constantly shifting stesses on the fasteners- eventually they can begin to "work", the sealant around the fasteners fails, and water gets into the core. If I were to build it with a plywood core, I'd overdrill the holes and fill with thickened epoxy, then re-drill for the fasteners as has been discussed here before.

Edited to add:

These are pictures of the results of the thermal expansion/contraction of Starboard/Seaboard. No, the fasteners were not overtightened at installation. Fortunately it splits cleanly, I'm going to glue the pieces back together and throw in a dummy screw head and drill for new fasteners nearby. This time I'm going to overdrill the holes...

I don't know what that is but it appears thin and brittle.Those cracks also look like stress failures.I say that because it broke away entirely like plastic.

Like I said earlier, you simply can't overdrill holes for a swimdeck.It'll be as sturdy as a folding ladder.

 

[shore]

The access panel at the underside of my radar arch has cracked right across from screw hole to screw hole. I would like to remove it and glue it back together this spring. Please let me know what adhesive you wind up using, I've heard that these products don't accept most glues and sealants.

If itis King product go to their site and they have some stuff listed that has worked.

 

[Danny Troy]

Well, I just did a search and couldn't find any difference between Starboard and Seaboard. So Shore, if one of us gets any cracking lets post to warn others. I would imagine drilling so close to the edge might be another reason for the stress cracking. Luckily, we didn't do that on our platforms.

Hey, check out the DIY platform this guy made from generic HDPE. Definitely bigger than your's, I think.
http://www.baylinerownersclub.org/forum/showthread.php?t=39047

 

[shore]

That's a bit much.....like a porch back there.He does have vents though.I can only imagine how bad that catches water.

 

[Dasch Boat]

If itis King product go to their site and they have some stuff listed that has worked.

My apologies if I am steering this thread away from the swim platform issue but you may need this info down the road. King responded to me by e-mail and they list two products that "some people have had success with" (3-M Scotchweld DP-8005 or Adhesive Methods and Technologies 7540-AB). Has anyone had any luck with these ? My repair is in a highly visible location so it needs to look decent.

 

[Danny Troy]

Whatever you use, I'd be sure to roughen up the area very well, and clean it with acetone. I'd also, if possible, use a tiny drill bit in a Dremel and drill many holes to give the glue more "bite". I do this on surfaces that need extra hold, or surfaces that the glue may not adhere to well enough.

As far as gluing Starboard, I used Gorilla glue, but the bond wasn't strong. I actually added screws to help the glue, but it was in an area that wasn't visible, so looks didn't count.

 

[skibum]

I don't know what that is but it appears thin and brittle.Those cracks also look like stress failures.I say that because it broke away entirely like plastic.

Like I said earlier, you simply can't overdrill holes for a swimdeck.It'll be as sturdy as a folding ladder.

Shore, this is the point that he is trying to make. That is real Starboard. When materials that expand and contract at different rates are firmly attached to each other, something is going to stretch, bulge, pull apart, or break to accomodate the changing sizes of the parts. It has to. The forces generated can be incredible. The goal is to anticipate this, and account for it in the design. Go to a woodworking forum and read up about "wood movement". You have the same issue with Starboard. The only significant difference is that the Starboard will expand or shrink uniformly in all directions whereas wood expands and contracts primarily across the grain with very little along the direction of the grain.

I disagree with the statement that "you simply can't overdrill holes for a swimdeck". You can, you should, and you must. The holes in the mounts should be regular size. The holes in the Starboard should be based on the amount of expansion / contraction. Simply calculate the amount of expansion for a reasonable range of temperatures and add that to the hole sizes. The best way to do this would be to drill the oversized hole for the shank of the bolt to go all the way through the Starboard and then take a larger bit and make a hole that only goes deep enough to get a washer and the head of the bolt below the top surface of the platform. Obviously, the top hole needs to be as large as whatever washers you use + the amount of movement that you calculated. Since Starboard is waterproof, the open area around the bolt shank will not rot. The washers and the heads of the bolts will hold the platform securely in place, yet when the Starboard expands or contracts it will be able to "slide around" under the washers without tearing anything else apart.

The forward edge of your platform is firmly affixed to that bracket on your transom. It (the front edge) ain't going to move. That is your anchor point. If the bolts at the top of the braces hit the platform at a point 24" (for illustration purposes) away from the anchor point and are not overdrilled, what will happen if the Starboard expands 1/8"? The bolt going through that brace is fixed in space at the 24" point. The front of the bolt is now trying to hold a "hole" that wants to be at 24 1/8" away from the anchor point at the 24" position. It is pushing the tops of your braces backwards. The only remaining questions are, how much force is there and which component will "give" to accomodate it? Tobnpr's pictures show that the force is strong enough to cause the Starboard to tear itself apart. Lucky for him that the fiberglass and screws holding the part in place were stronger than the Starboard or he would have been repairing his boat instead of the part. So, if you were to pull that bolt at the top of one of your braces out 1/8" with a chain attached to the bumper of your truck, what would "give"? The bolt going through the platform and the top of the brace are the parts trying to move. The brace, the bottom of the brace, the screws holding it to the transom, and the fiberglass surrounding the screws in the transom are the parts trying to stop that movement.. The curves at the top of the braces might flex enough to accomodate the movement. If not, then I suspect that the screws would pull out of the transom. How comfortable would you be exerting enough pulling force on the top of one of your braces to move it 1/16" towards the rear? Think about it. If that Starboard expands, that is exactly what it will do. If it contracts, it will be pulling it backwards.

I am not bashing either one of you or your platforms. I think both of you guys did a bang up job that looks great. I just think that you should protect your investments by addressing the movement issue that does in fact exist. You can do this easily without any additional cost unless you need to buy a bigger drill bit...

 

[tobnpr]

The material is 1/2" black Seaboard. As far as distance from the edges, I thought it was adequate- it's really not that close.

The corner in the center picture is already glued back with clear Lifeseal. Yeah, I know it's not supposed to work, but so far it has held- of course, there's no "pressure" on it, just holding it in place. One of the structural adhesives mentioned above is needed for a real repair.

I'm still a big fan of the stuff, but this is one drawback. Because of it's physical properties- it does NOT compress (I used it for shims in mounting a new inboard) , when there's enough stress placed on it, it will crack, rather than "give". In the future, I'm going to oversize the pilot holes as well as the countersinks.

EDIT: Skibum, you and I were typing at the same time. Excellent post, well said. I was only trying to bring this issue to light, but get " I don't buy it" despite the manufacturer saying it's so... can't change physics, any more than you can enlighten a stubborn mind, I guess.

 

[TheLucille]

I don't know what that is but it appears thin and brittle.Those cracks also look like stress failures.I say that because it broke away entirely like plastic.

Like I said earlier, you simply can't overdrill holes for a swimdeck.It'll be as sturdy as a folding ladder.

You can, and should. Water ingress is the enemy.

A bolt is not typically designed to be snug in the hole and support the load via resisting shear. It's designed to pull one surface against another, so that the friction between the two holds them "up".

I'm sure the black starboard exacerbates the expansion issue. You'll have less of a problem with white. Starboard (and the cheaper, almost identical Seaboard) is HDPE which is pretty stable stuff.

That being said, I'd go the plywood/fiberglass route. Properly built, it would last far longer than you'll ever own the boat. Look at many plywood transoms, the ones that rot are from having poorly sealed holes, but the vast majority are still fine at 20 and 30 years old. And some of them sit in the water 24/7.

 

[shore]

The material is 1/2" black Seaboard. As far as distance from the edges, I thought it was adequate- it's really not that close.

The corner in the center picture is already glued back with clear Lifeseal. Yeah, I know it's not supposed to work, but so far it has held- of course, there's no "pressure" on it, just holding it in place. One of the structural adhesives mentioned above is needed for a real repair.

I'm still a big fan of the stuff, but this is one drawback. Because of it's physical properties- it does NOT compress (I used it for shims in mounting a new inboard) , when there's enough stress placed on it, it will crack, rather than "give". In the future, I'm going to oversize the pilot holes as well as the countersinks.

EDIT: Skibum, you and I were typing at the same time. Excellent post, well said. I was only trying to bring this issue to light, but get " I don't buy it" despite the manufacturer saying it's so... can't change physics, any more than you can enlighten a stubborn mind, I guess.

I just can't agree with this.My starboard deck is soft.It absolutely compresses.I can run a screw past flush and nothing is close to cracking.I put over 100 SS screws into two sheets of the stuff and nothing has cracked.

Now that I think about it, I have a sub enclosure face plate on the boat made out of a piece of my leftover 3/4".It's screwed right to the fiberglass.It has 16 SS screws in it and they are close to the edge like your black piece and none have cracked.

Maybe the stuff has an ideal working temp of hotter the better.Maybe the thickness has something to do with it.I don't know.

 

[shore]

You can, and should. Water ingress is the enemy.

A bolt is not typically designed to be snug in the hole and support the load via resisting shear. It's designed to pull one surface against another, so that the friction between the two holds them "up".

I'm sure the black starboard exacerbates the expansion issue. You'll have less of a problem with white. Starboard (and the cheaper, almost identical Seaboard) is HDPE which is pretty stable stuff.

That being said, I'd go the plywood/fiberglass route. Properly built, it would last far longer than you'll ever own the boat. Look at many plywood transoms, the ones that rot are from having poorly sealed holes, but the vast majority are still fine at 20 and 30 years old. And some of them sit in the water 24/7.

water ingress to where?

 

[shore]

Shore, this is the point that he is trying to make. That is real Starboard. When materials that expand and contract at different rates are firmly attached to each other, something is going to stretch, bulge, pull apart, or break to accomodate the changing sizes of the parts. It has to. The forces generated can be incredible. The goal is to anticipate this, and account for it in the design. Go to a woodworking forum and read up about "wood movement". You have the same issue with Starboard. The only significant difference is that the Starboard will expand or shrink uniformly in all directions whereas wood expands and contracts primarily across the grain with very little along the direction of the grain.

I disagree with the statement that "you simply can't overdrill holes for a swimdeck". You can, you should, and you must. The holes in the mounts should be regular size. The holes in the Starboard should be based on the amount of expansion / contraction. Simply calculate the amount of expansion for a reasonable range of temperatures and add that to the hole sizes. The best way to do this would be to drill the oversized hole for the shank of the bolt to go all the way through the Starboard and then take a larger bit and make a hole that only goes deep enough to get a washer and the head of the bolt below the top surface of the platform. Obviously, the top hole needs to be as large as whatever washers you use + the amount of movement that you calculated. Since Starboard is waterproof, the open area around the bolt shank will not rot. The washers and the heads of the bolts will hold the platform securely in place, yet when the Starboard expands or contracts it will be able to "slide around" under the washers without tearing anything else apart.

The forward edge of your platform is firmly affixed to that bracket on your transom. It (the front edge) ain't going to move. That is your anchor point. If the bolts at the top of the braces hit the platform at a point 24" (for illustration purposes) away from the anchor point and are not overdrilled, what will happen if the Starboard expands 1/8"? The bolt going through that brace is fixed in space at the 24" point. The front of the bolt is now trying to hold a "hole" that wants to be at 24 1/8" away from the anchor point at the 24" position. It is pushing the tops of your braces backwards. The only remaining questions are, how much force is there and which component will "give" to accomodate it? Tobnpr's pictures show that the force is strong enough to cause the Starboard to tear itself apart. Lucky for him that the fiberglass and screws holding the part in place were stronger than the Starboard or he would have been repairing his boat instead of the part. So, if you were to pull that bolt at the top of one of your braces out 1/8" with a chain attached to the bumper of your truck, what would "give"? The bolt going through the platform and the top of the brace are the parts trying to move. The brace, the bottom of the brace, the screws holding it to the transom, and the fiberglass surrounding the screws in the transom are the parts trying to stop that movement.. The curves at the top of the braces might flex enough to accomodate the movement. If not, then I suspect that the screws would pull out of the transom. How comfortable would you be exerting enough pulling force on the top of one of your braces to move it 1/16" towards the rear? Think about it. If that Starboard expands, that is exactly what it will do. If it contracts, it will be pulling it backwards.

I am not bashing either one of you or your platforms. I think both of you guys did a bang up job that looks great. I just think that you should protect your investments by addressing the movement issue that does in fact exist. You can do this easily without any additional cost unless you need to buy a bigger drill bit...

You don't have to explain to me what happens.What you have to explain is why it didn't crack.

What you are saying is just to be safe lets pull all those screws out and over drill and use bolts washers....Umm no.I have 6 visible heads countersunk on the topside.I'm not going to add 100 more for insurance.The entire deck would have to come off.I've already mentioned my mounts,deck to starboard, to the boat are over drilled purely by chance.Around a 1/4" on the fiberglass side.The only screws that are not over drilled are the side mounts and that is because they are not thru-bolted.I can certainly alter those.

I never said the stuff does not expand contract...no where did I deny that.Just that maybe they play it a bit safe.I agree the stuff moves BUT I want to know why mine does not.I've done something different that works so far and that would be great to understand.

 

[tobnpr]

No question the black exacerbates the problem. Gets hot enough to fry an egg on in the sun. I've also had similar failures with white, tho. I wish I could associate the failures with a specific event, but I can't...

It is interesting that two of the three cracked areas are in the identical location- at the end of the boards in the upper corners.

I took the boat out for a spin this morning to breathe some salt air and clear out the cobwebs- and it seems logical to me that the more fasteners that are used, the better (to a point). Lets say you calculate 5/8" of change over the entire length due to temperature extremes. If you only have four fasteners drilled over that length, that's over 1/8" that each fastener must "absorb". Now if you have 16 fasteners, that becomes only 1/32" inch for each fastener- assuming that they're spaced evenly, and that the material changes dimensionally in a mol linear way. Seems it would be best to do the initial fabrication with the material rather cool; if you live up north where the temp hits 0 degrees in the winter, and 100 in the summer heat, you'd want to do it at 50 degrees (ideally), or at least room temp.

I think that on a swim platform application where you have a limited number of fasteners, like the four mentioned above- overdrilling by 1/8" or so would not make it overly "sloppy" or have the swim platform "sliding around" to the point where it would be noticeable- it's only 1/8"...and I don't think it would even be noticeable.

In any case, the project looks great. Please let us know at the end of the season if there have been any issues. That's what this forum is all about- sharing information and learning from our mistakes, right?

 

[shore]

I'm just curious as to why mine has no issues.It's been 10mths since I made that deck with the deepest of cold and the hottest of sun.Then again, the deck never got hot to the touch in daytime sun.There was a noticeable temp difference even between the original deck and the starboard.The fiberglass was plain and simple hotter.

Maybe it is all the screws that makes it hold its size.

I'll certainly keep and eye on mine to see what does or doesn't move.

 

[Danny Troy]

Yes, lets put this issue to rest. We have been forewarned, but we're willing to take our chances. I'll keep a close eye on it, and I can check for expansion by comparing the changing angle, relative to the existing platform. I really would be surprised if the 3/8" stainless bolts pulled out of the transom, complete with wide 1/4" thick backing plates. Anyway, I will definitely post if there is any indication of cracking.....I promise :grin:

 

[skibum]

You don't have to explain to me what happens.What you have to explain is why it didn't crack.

What you are saying is just to be safe lets pull all those screws out and over drill and use bolts washers....Umm no.I have 6 visible heads countersunk on the topside.I'm not going to add 100 more for insurance.The entire deck would have to come off.I've already mentioned my mounts,deck to starboard, to the boat are over drilled purely by chance.Around a 1/4" on the fiberglass side.The only screws that are not over drilled are the side mounts and that is because they are not thru-bolted.I can certainly alter those.

I never said the stuff does not expand contract...no where did I deny that.Just that maybe they play it a bit safe.I agree the stuff moves BUT I want to know why mine does not.I've done something different that works so far and that would be great to understand.

No... I did not mean to suggest or imply that that you need to remove the 100 screws. The way that I understood your construction, the 100 screws were used to laminate the 2 sheets together, correct? All of them are fine. Both sheets will expand or contract at exacty the same rate. There will be no additional (horizontal) forces exerted on the screws holding them together at all.

The sum total of the changes that I would have made would be to make the 6 holes where the platform sits on the braces at the back a little larger. That would be it.

You don't get the same extreme temperature swings in Florida that you would in Chicago or Maine. You might never have a problem. Tobnpr's parts were black, so they absorb more heat more quickly from the sun than white parts would. At 1/16" per 40 degrees per foot, you will see just a little over 3/32" of movement at the 20" mark, and right around an 1/8" at the 2" mark. If you get 20 degree nights in the winter and 100 degree days in the summer, that is an 80 degree swing that will cause 3/16" to 1/4" of dimensional change every 20" to 24". Further north, it is not uncommon to see sub zero in the winter and 100+ in the summer making for even more movement. The 3/4" thickness dimension change will be minimal and the combined strength of the 100 screws holding the pieces together should be sufficient to prevent any problems there.

Finally, I apologize if I offended you. I am an amateur woodworker and I have already learned a few lessons the hard way. Movement is no joke, and the forces created by it can be extreme. I stated before that I thought your platform came out really nice. I like it. I was not suggesting that you needed to start over. I was simply suggesting oversizing the 6 holes at the top attachment points of the braces to prevent them from becoming levers and amplifying the forces applied at the top of them to the bottom mounts. You could accomplish the same thing by oversizing the holes where it attaches at the front edge. Whichever is easiest. My only concern is that if everything is assembled tight, even 1/16" of movement will put something under stress. Tobnpr's pics just illustrated that fact that the forces became strong enough to cause the part to self destruct. It is pretty easy to tell that the part shrank and applied all of the force to the outside of the screw holes. The weakest part gave in. His part was also only 1/2" thick. If it was 3/4" thick, it may have been strong enough to bend the screws or rip them out of the fiberglass altogether.

I'll refrain from further comment on this thread. I was just trying to be helpful. :huh:

Michael

Edit... I previously missed where you mentioned that the holes on the fiberglass side were oversized. That alleviates my concerns. You have the necessary room for movement accounted for back there. If you say that there are only 2 that are not, and that they are easy to get to, then my advice would be to do so. I would still consider enlarging the other 6 holes at the top of the braces though because the expansion and contraction may cause a little spreading out or pulling together force between the braces. Better safe than sorry.

 

[TheLucille]

water ingress to where?

Sorry, my confusion. I thought the overbored holes was referring to the transom mounting. My bad.