solid v/s sandwich question.

[jeffwholmes]

Ok everyone I’m sorry for all of the questions but I am trying to finalize my plan so I can buy some materials this week. So please bear with me.

Which is lighter solid ¾ walls or sandwich construction?

I think that I’m going to build a 5’x9’ generic benroy profile, I currently have a 94 Olds cutlass supreme 3.1L rated to tow 2000lb.

I want to put a 14’ aluminum boat on top of it, I will build a rack that attaches to the frame for that. The boat weighs approximately 255 lb. / 116 kg. The boat motor witch I will need to make a mount for attaching it to the trailer weighs approximately 110 lb. / 50 kg. So I need to keep my weight in check.

Also I know that 2000lb might be a little generous for the olds, we will see. I’m an old pro at towing. I drove wrecker for 6 or 7 years. 1 tons for the small stuff and a tandem axel Mack for the big stuff (road tractor and trailer combos)

Any Ideas as to what a 5’x9’ would weigh of either construction?

I will be towing with an s-10 in the future, but for now the cutlass is all I have.

Thanks Jeff.

[ARKPAT]

I wish I was far enought and have run the trailer up and down the highway enought times to give you a real answer. I'm tring to build with Insulated door blanks for construction. You can build lighter like Roly's build or some others. I'm not sure how my build will weigh and do traveling down the road but I will find out in a couple of weeks.


It will be lite!

I will see what happens and take pictures and give a report back to the group.



Pat

[Nitetimes]

Take this for what it's worth but.... it seems like the average for that size comes in between 800-1000 lbs. It depends a lot on how you build but that is what quite a few folks are reporting for weight.

[jeffwholmes]

Thanks Rich.

If it came in around 1000 then boat, motor and gear should be 1500 to 1600, not to bad and I won’t have the boat all of the time.

Jeff.

[jeepr]

I would say a sandwiched wall would be lighter. My walls are approx. 5'x9', 3/8 outside 3/4 ribs with luan on the inside. I could move them around no problem. They sure felt lighter than a 4'x8' sheet of plywood.

If you are going for light weight, I have read about people using 1/4" ply outside and 1/8" inside on a framed wall. Especially if you plan on using aluminum or filon covering the outside.

[jeffwholmes]

Thanks jeepr, though I have changed my mind. I will be going with ¾ birch sides using a spline joint to get my 9’. The good side will be to the inside. I will be using epoxy on the outside and painting it. Also I read thru a bunch of posts last night, slow night at work. Any way one person I can’t remember who but the weight of the sandwiched panels was almost equal to the ¾ plywood.

Jeff.

[SteveH]

Jeff,

I have a Benroy (sort of) 5 X 9' teardrop built with 3/4 ply sides and it weighs approximately 1250. The sandwich would be a little lighter, but with the load you want to put on top, I would also be concerned about the strength issue. I believe the 3/4 would be stronger, but I could be wrong.
Good luck with whatever you decide to do.

[asianflava]

. Any way one person I can’t remember who but the weight of the sandwiched panels was almost equal to the ¾ plywood.

I built mine with 1in sandwich walls, I figure it to be about 20%-30% lighter than solid 3/4in ply (depending on how much stud work is in it). Sandwich construction also means that it is insulated which keeps out the sun and the cold. My 5X10 weighed in at 1150lbs which includes the a/c, battery, microwave, stove, and a relatively heavy memory foam mattress, ready to go just add food clothing and bedding. I also keep the EZ-up, chairs, etc. in transit so I figure that it's about 1500lbs loaded.

I'm pretty sure that I could have it under 1000lbs if I used a lighter mattress, a smaller battery, less complicated cabinets, no a/c, and no aluminum skin.

[bobhenry]

I built Chubby with 1/2 osb sides then 1/4 luan veneered on both inside and out. If I did it again I would use a/b grade 1/2 plywood and save the veneer step outside. The solid material is much quicker. I had both sides cut and standing in one afternoon. I stood the sheets up and planned the breaks to fall at the door seam and the galley wall. This allowed me the 5' 6" side heigtht. I used 1x4's to gusset the sheets together this left a 3/4" void for 3/4 foam and electrical chases. I used the 1/2 depth electrical boxes for the switches and plug ins. The 1x4 were the nailers for the luan inside. Just my $ .02 worth !!

[jeffwholmes]

SteveH, thanks and I really like you’re almost benroy. Yours is probably the profile I like the most, I just hope mine turns out nearly as nice. What is different about your profile?

Also I understand what you are saying about the strength, but when bringing the boat along I plan on fabing some mounts to the bottom of the frame that will accept square tube and bolt a rack to the frame front and back. The boat won’t rest on the tear.

And thanks for your information to asianflava.

Well it is off to bed, I’m on night shift this month. And I’m going to pick up my birch in the morning after my shift.

Thanks Jeff.

[jeffwholmes]

Thanks henry, I appreciate all of the info from everyone.

Jeff.

[MrBuzz]

My 4X8 Gen-Benroy is built with 3/4" plywood walls and floor. I used the Harbor Freight folding trailer. It is built like a tank...no flex in the sides at all! Solid walls also definitely speed the build process too. When I do another one I will go with 5/8 or 1/2 walls to save some weight. But even with the 3/4 solid walls the TD weighs less than 700 lbs.

[angib]

the weight of the sandwiched panels was almost equal to the ¾ plywood

Yes, it's quite easy to get a sandwich panel to weigh nearly as much as a solid 3/4" panel. Here's a table of weights (in pounds per square foot) of different types of construction:

http://www.angib.pwp.blueyonder.co.uk/t ... t-data.pdf

There isn't actually a table for completely unstiffened ply - at 3/4", you wouldn't need any/much framing. 3/4" ply weighs about 2.9 lb/ft2 whereas inner and outer skins of 1/4" ply over 1x framing will weigh between 2.3 and 2.6 lb/ft2, depending on how much framing there was. So the solid 3/4" walls would be around 30 lb heavier than 1/4" sandwich walls - but this is just for the walls - if you used solid 3/4" everywhere then maybe the difference would be maybe double.

However if you went to 1/8" skins, the sides would weight 1.4-1.7 lb/ft2 - about half the weight of the solid 3/4" ply and saving maybe 100 lb just for the sides or around 200 lb for the whole body.

Any wooden construction will be strong enough to carry a 250lb boat on top, as long as it has a complete galley bulkhead (to make a strong box to resist racking). The only place where you could have a problem is where the boat racks attach to the body - you would need plenty of wood there to spread the load out into the surrounding structure. If you went 3/4" solid, adding 3/4" doublers where the racks fit would be all that's needed, if that.

Andrew

[tomsglr]

Mine is 5' 3" wide \ 5' high\ 8' long. I used a Harbor Freight trailer. 3/4" Advantech flooring. The walls and ceiling are 1-1/2" thick with 1" foam and 1/2" fiber insulation board. The outside and inside are covered with probably 1/8" paneling. With the AC installed it weighs approx. 1100 lbs. What trailer are you putting it on?
Tom

[jeffwholmes]

MrBuzz and Andrew, thanks.

tomsglr, I will be building my trailer out of 2”x2” 1/8 angle. Still thinking about the tongue, I will be building a tongue box so I will make my tongue 48”. I was going to use 2”x2” 3/16 sq. tube but by Andrew’s calculations I don’t think it will be strong enough.

I am going to estimate my overall weight at 1500 lb. / 682 kg.
Strength needed is 0.5 x 1500 = 750 x 48 = 36,000.

The 2”x2” is only rated at 20,900 lb/in vertical capacity, think I could use 2.5”x2.5” it is rated at 35,600 lb/in vertical capacity.

Did I get that right Andrew?

Jeff.