Custom swim platform

Juergen

Juergen

Member
Sep 25, 2013
195
Greenville sc
Boat Info
400 DB 2001
Engines
454's
Hi guys,
I'm trying to design and build a swim platform for my 370. The overall dimensions are about 4'x10' and I'm planning to have about 5 brackets supporting the platform in a roughly 45 degree angle. I'm using the king starboard material with 1.5" thickness, it is commonly used for platforms like this.
I'm going to use for support brackets a 1" diameter 0.064" wall thickness unpolished 304 SS tubing, does anybody know if the 304 is corrosion resistant enough for freshwater or shell I go to a higher grade or increasing the wall thickness of the SS tubes?
The mounting concept so far is to bolt about 8" of the platform underneath the integrated swim platform and supporting it in addition with the 5 mentioned SS brackets, each is about 3-4 feet long. I'm purchasing a 20' long tube and cut each bracket as necessary. The ends I plan to squeeze flat drill a hole in and bend it to the right angle.
See attached pics for a better understanding. If you have any concerns, commends, thoughts, etc. please let me know.

Cheers.
Juergen
 
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My concern is the amount of flex you will experience with three or four people walking on the 1.5" starboard.
 
Good point but I will try it out before I put it back in the water and if that's the case I can add more support brackets.
 
Juergen said:
Good point but I will try it out before I put it back in the water and if that's the case I can add more support brackets.
Click to expand...

Support brackets will not stiffen the material and will transfer stress to the attatchment points. I wonder why some company doesn't challenge the platform market with a relatively inexpensive starboard platform? Could it be the material is not suitable for it? Does anyone make them for even small vessels? If not, why not?

The material specs are here http://www.kingplastic.com/products/all-products/king-starboard-family/king-starboard/

MM

It did later see that they do offer narrow "platforms", that appear to be half the size of the plans above, for sale made of Starboard.
 
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Wait a second.... I missed that you were making this out of stare board... You need to consider the thermal expansion of the material. This stuff has a high expansion coefficient if I remember correctly. I would think that would make it very difficult to use. I remember someone doing a side in the cockpit and actually had to slot an area for the screw to go into because it was shearing the screw heads off.
 
Wow, I didn't consider that... I need to find out how much it will shrink and expand. What material would u recommend?
 
Have you also considered how slippery the starboard might be when it is wet?
 
For the size you want, engineered frame with fiberglass, which is why I spent the bucks at Swimplatforms.com.

There is no free lunch.

MM
 
+1 for the swimplatforms.com route! Just my .02 but I love mine!
 
Starboard is slippery when wet,it also gets a bit flexible when its in the sun,and the screws will tend to strech the holes they are in,i wouldnt do it.Also 4 ft is a lot of added platform ,are you sure it wont drag while getting on and off plane,as that would shorten the fasteners ability to hold in the starboard also.
 
I wouldn't buy the boat after seeing it with all the bracing drilled into the back of the boat. It may look good on day one, but what about season 3, 4, etc? I would go with the norm. It looks factory and IMO, helps retain resale value.
Sea_Ray_350_&_370_'90-'97-2a_(2).jpg
 
Juergen said:
See pic below. Do u think supporting it with a u-channel 2"x2" would stiffen it enough?
Click to expand...

Yeah, I am sorry but I wouldn't suggest using a piece this large to try and do what you are doing. You can't contain what the material will want to do. Adding the brace across the beam will stiffen it transversely but it will do nothing with the length that the material will grow and shrink and weaken around the attachment points. As stated previously you may love the added platform but I can tell you that it WILL hit you in the resale value, and yes in year or two I would imagine that the stresses will catch up with the entire apparatus.

I have actually contemplated building a swim platform for mine as I like this type of work and I am always up for a challenge (the problem is finding the time). If I were going to "build" my platform the way to do it is like the link I shared with 390x. He did a fantastic job and I would only change one small detail. I would use Divinycell instead of the lumber. Here's a link to information about the different materials →http://www.matweb.com/search/GetMatlsByTradename.aspx?navletter=D&tn=Divinycell®← I know he did a great job and sealed it up very well but as an engineer I always think "what if". If the foam gets wet it will never rot or have ill effects on it...

Swimplatforms.com. I know many people on here have them and have seen several up close. They are very well made and are easy to install. Yes, they are $$$ but then again its a boat and whats say 3 boat bucks to have something that will help the resale instead of hurt it and you know for sure will be safe and reliable. The only reason that I wouldn't do one of these on my boat is because I have a classic Sea Ray and I don't think the style looks right with my sharp lines and I want to keep my woodwork.

What ever you decide we are here to help but I would strongly steer you away from starboard for this particular application.
 
I'm certainly not an expert but my knife making research as given me a bit of understanding of Stainless steel. If you have SS that is not magnetic then you are generally using 300 grade steel which is low in carbon but high in chromium, nickle and other anti oxidizing materials. This makes them great for rust resistance but poor for cutlery. Cutlery SS is in the 400 range and the carbon content is much higher. Say a 440C SS is around .95% carbon. This however does make the steel more susceptible to rust. This SS is magnetic BTW.

If you were making a knife and used and 440SS compared to 430SS your knife would be worth up to 30% more in value due to the better steel. Most production knives are made from the lower grade SS as it is easier on the dies that punch them out. Custom knives either handmade or limited production are in the 440C SS range and offer great strength and hardness to both hold an edge and be flexible. Many knives like the popular SOG brand are 430SS that keeps them cheaper to manufacture and less expensive to sell.

The new SOG Tanto tactical sells for 190US and uses AUS - 8 SS which is about .75% carbon or around a 430SS. That same knife if I made it out of 440C SS would cost you double.

Since 440C(chromium) has a high chromium content it does resist rusting better than 440A SS though both are excellent for knives.
 
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A starboard rep told me that he wouldn't suggest making a large platform with his product. He said it would sag under it's own weight, and that it would expand and contract way too much. It will also be very heavy.
 
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A couple years back I posted my swim deck build out of composite lumber instead of teak or cedar for my classic.(see profile pictures) The material has held up well however I needed to add a couple more supports as it looses it's rigidity over time and with use. The thing still looks good but a sag at the swim ladders is very evident.

I'm just preaching to the choir here but any "alternative" materials need to be investigated. Which is what you are doing with this thread.:thumbsup:
 
Thanks a lot guys!!! U brought up a lot of valid points and I'm either going to purchase one of Swimplatform.com or try the "do it yourself way" like 390x did, what seems to be a pretty intensive project. Need to do some more investigation about the gel coating part, I love wood work but the gel coating part of it is still a little scary to me... Any input about the gel coating, glazing etc. ?
 
Juergen, are you boating on Hartwell or Keowee? CSR tries to have a raft up on Keowee or Jocassee on labor day every year. Watch for it this year.
When we lived in NC we boated on Keowee. I love that l
 
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