Cradle construction question

[Sefuller]

I need to have a storage cradle built this year, and have been working with a local welder, but would like a second opinion on the strength of what I am proposing. I have an Oday 34, the factory weight was 11,500. I plan to construct the cradle using 3x5 rectangular steel tubing, could be either 3/16 or 1/4" thick. The base will be 14 feet long and 6 feet wide, with three cross members of the same material perpendicular to the sides, underneath the keel. The keel is approximately 6 feet 6 inches long, and I plan to space the cross members 2 feet apart from each other, roughly centered in the 14' length and centered under the keel. I don't have enough engineering background to know how to use the tubing calculators I find online, nor do I have an idea of what reasonable deflection would be. When the boat is stored, the cradle will be supported on wood blocks, but when the boat is being moved around the yard, I can't guarantee that it won't be supported only near the ends of the cradle, so I'd like to know what I need for a worst case scenario. I am guessing if my proposed structure is not adequate, it would only be the long side pieces that would need to be more substantial?

Anecdotally, it appears what I am planning is more sound than about 90% of the cradles I see in most yards!

Thanks for any advice,
Scott

 

[Don Crowther]

Scott
I've attached plans for a cradle for a Hunter 34. Similar size and weight. It's not made of tubing but 6 inch channel. Hope this helps

 

[Sefuller]

Looking for feedback on the rectangular tube...

I appreciate the sketch of your cradle, but would still like to know if the 3x5 rectangular tube as specified would be appropriate for this application.

Thanks,
Scott

 

[Brian D]

Don, I have always wanted to know the distribution of weight that is on the keel and on the pads. Is there more on the pads than the keel? Even-steven? or is there more on the keel? I would fear that too much weight on the keel could push the keel through the boat.

 

[Don Crowther]

Brian;
I've always had all the weight on the keel. The pads are only to stabilize the boat so it doesn't tip over. Lots of boats sit on the ground with only stands keeping them upright.

What I do is tighten the pads against the boat so it doesn't rock and sits firmly in the cradle. The pads are under bulkheads so they have a good solid base. Hope this helps.

 

[DougM]

I have seen a number of cradles constructed using 6 inch channel iron rather than rectangular tube. Crossmembers are also channel iron, typically spanned with a flat section often not more than 3/4 plywood. Uprights are square tube fitted with pads for the hull. The pad supports should be planned to line up with strong points in the hull such as the interior bulkheads. Also plan to keep the clear of the locations for the lifting slings .11,000 pounds relatively speaking is not all that heavy and should not require rectangular tube.
Get some input from your yard crew as to how they prefer to handle and transport the cradle, make it easy for them for such things as potential fork lift pockets or bracketing for their yard trailer. The cradle needs to be strong, but not overbuilt.

 

[tommays]

Should be plenty of used or able to look at and copy JOWI up you way
http://www.jowi.com/location.html

 

[higgs]

Don, I have always wanted to know the distribution of weight that is on the keel and on the pads. Is there more on the pads than the keel? Even-steven? or is there more on the keel? I would fear that too much weight on the keel could push the keel through the boat.

Weight should always be on the keel. If weight is on the pads, damage can be done to the hull which is not designed to support the weight of the boat.