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needs help Idaho Used Aluminum Boat?

Question:
needs help Idaho Used Aluminum Boat? Could any of you offer me some design tips for welding a trailer together for a Phil Bolger Idaho? It is 31'x5', flat bottomed, weighing 1200 lbs. I am purchasing a MIG welder (any suggestions?), learning how from a book. Info. on the design of the trailer, the grade of steel, number of axles, anything would greatly be appreciated.


Answer:
- and that's what its worth, and what it should be warranteed for. I get nervous giving advice to others on the subject of boat trailers, steel construction, and welding, but here goes. All liabilities are yours and yours alone.

1. For a boat this size your biggest challenge will be supporting the span of the steel, rather than the weight of the boat.

2. I've built many trailers using a "3 scantling" rule: The first number is the size of the channel used for the two main longitudinal members (the ones on the outside of the trailer), the second number is the one for the trailer's cross members, the third number is the for the trailer's longitudinal stiffners (the parts that are inboard of the main longitudinal members). Example: 6, 5, 4 means a trailer with: 6" main longitudinals, 5" cross members, and 4" stiffners. I've used a 6,5,4 for boats 22 to 26', 5,4,3 for boats 18 to 22', and 4,3,2 for boats <16'.

3. If this was a routine 24' to 28' fishing boat with an 8.5' beam, 7,000 to 12,000 lbs, I would use a 6,5,4 trailer, with three 5,000 lb axles, surge brakes on the back two axles. Your boat sounds like nothing I've ever seen - 31'x5', 1200 lbs? What's it made out of, papier mache? I'm afraid any trailer strong enough to support its own weight would be so stiff that it would shake your boat to pieces going down the road. If on the other hand its 12,000 pounds you can probably use a 6,5,4 trailer, with two sets of stiffners and perhaps a 6" centerline longitudinal - but that's only a guess. I've never built one that size.

If your boat is 31' long, 12,000 pounds I recommend you take your plans to a trailer outfit and ask them to draw up some plans. This is a big project that needs more brain power and concerted study than your likely to find in a discussion group. The last thing you want is some cyberopinion that results in your boat doing a belly flop down the interstate. Oh, also make sure you get a MIG set up that can weld 1/4" steel, with a decent duty cycle (>30%) - that means a real welder (Lincoln, Hobart, Miller) - not a Harbor Freight and Salvage Chinese Special.

- Yes, the weight is only 1,200 pounds. The boat is a plywood flat bottom hull design, a skiff if you will, a big flat bottom canoe. You can see it at Common Sense Boats, http://www.common-sense-boats.com/boats/Power_Boats/idaho.htm .

You certainly sound like you know your stuff. Thanks for sharing your insight.

One of the reasons I chose to build Idaho is because of its weight, thus I am concerned that I build a trailer as minimal in that department as well. As you pointed out, the 30' span is the challenge.

What do you think?


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