SkipJack 20 custom trailer

[sprince]

Current trailer for my SkipJack 20 is painted steel, not dead yet but I'm thinking about a replacement trailer at some point. The way I use the boat I need to lower as much as possible, another 4 inches would be ideal. This trailer has leaf springs and there is 6 inches between the tandem axles and the lowest part of the Vee in the hull. Also the trailer is short, the bunks stick out 1.5 feet past the last cross member on the trailer in the back. I want the crossmember right under the transom.

The cheapest most practical solution would be a used galvanized trailer that fits my boat size, but the best solution would be a turn-key custom aluminum trailer with torsion axles, allowing me to lower the boat on the trailer with a lower weight. But this is also the most expensive solution, I priced some and what I want costs more than my boat.

My question is, has anyone built a custom SkipJack 20 trailer out of aluminum I-beam, purchased the main components and assembled? Not saying I could do it but just curious if it has even been done. The price is certainly much lower than a turn-key trailer. I did a quick check at https://www.boattrailerparts.com and the parts alone, including the I beams (from a different source) is about 1/2 price of a new one. There are probably ways to get the parts even cheaper.

This is my initial concept...... pasted together a tandem axle trailer with torsion suspension onto the Skipjack 20 brochure pic, just thinking out loud

 

[Capt.C.Delany]

Do you have the equipment to bend the I-Beams?

 

[Hismosa]

Here's a thread to give you an idea of all the work involved.

https://www.thehulltruth.com/trucks-trailers/1153869-i-am-building-my-own-trailer.html

 

[NotAnotherProject]

good question on the I beams… I wouldn’t think they’d use a low temper on those, which would be the obvious material to bend. A good temper would be ideal for the trailer but those bad boys would crack…I’d bet they’re tempered after the bend. So bend the I beam? Maybe. Temper it? Hmmm…

 

[sprince]

I watched those videos, they really help. Besides the proper design, it really comes down to bending the I beams. Everything else can be purchased or fabricated from aluminum. Some of those trailers are welded together, but others are bolted together using either stainless or galvanized hardware.

But the two videos showed different ways to bend the I beams. This guy used a log splitter, and bent the beam at a single point. But the maximum bend angle might be limited because the I beam might crack.

This one is a video on how to do it using a Harbor Freight press. The low cost way. Basically same as above but lower cost, still might crack.

This is the expensive press technique: A more precise press and bending at multiple locations to produce a "curved" bend. I like this technique. If you look closely he marked out 9 points where he did the bending to make the radius.

You can see his marks on the beam where he places the block.

Next question, how to size the I beams, axles, etc?

 

[sprince]

Here is the original boat brochure, says the weight with engine (and stern drive I assume) is 3200 lb, and length is 20.5 inches and I just replaced the tank so I know it is 65 gallons.

So around 4000 lb with boat gear, ice, fuel.

Top and side views

 

[NotAnotherProject]

Here is the original boat brochure, says the weight with engine (and stern drive I assume) is 3200 lb, and length is 20.5 inches and I just replaced the tank so I know it is 65 gallons.

So around 4000 lb with boat gear, ice, fuel.

View attachment 1485041

Top and side views
View attachment 1485042

Did you see any details on the aluminum? 6063 T1?

 

[Hismosa]

Here is the original boat brochure, says the weight with engine (and stern drive I assume) is 3200 lb, and length is 20.5 inches and I just replaced the tank so I know it is 65 gallons.

So around 4000 lb with boat gear, ice, fuel.

View attachment 1485041

Top and side views
View attachment 1485042

I had mine weighed at Cabrillo as they launch the boat by straps. It weighed 4500. And that was no gear/ice etc.

 

[sprince]

Okay, then assuming ice and gear are another 100 lbs plus a factor of safety, then round up to 5000 lbs. That's the same as my current trailer, a trailrite with 5000 carry capacity and 6000 GVW.

So far I have 3 sources for I beams, all are aluminum 6061 T6, but I live in CA so shipping may be a problem:
American Metals

Eastern Aluminum Supplies

Industrial Metal Supply-closest to me, delivers, but not boat specific

 

[NotAnotherProject]

Okay, then assuming ice and gear are another 100 lbs plus a factor of safety, then round up to 5000 lbs. That's the same as my current trailer, a trailrite with 5000 carry capacity and 6000 GVW.

So far I have 3 sources for I beams, all are aluminum 6061 T6, but I live in CA so shipping may be a problem:
American Metals
View attachment 1485066
Eastern Aluminum Supplies
View attachment 1485067

Industrial Metal Supply-closest to me, delivers, but not boat specific
View attachment 1485068

Yeah a bought quite a few pieces for a build recently. The shipping is wild on price but a lot goes into it beyond the trucking.

If I missed it above I apologize but I’d call one of the mfg’s and find out what they use. You can’t get much of a bend on T6 without the risk of cracking. I’d see if you can get a tech on the line and verify they’re really bending T6 post-temper.

Edit - ah I see they’re advertising it for boat trailers. Well hopefully a mild bend on T6 is no big deal. I think the graduate process in the press is probably the safest. The log splitter is wild.

 

[sprince]

Now I'm trying to figure out what size I beam to use, I started with 6 x 3 x .25 because this is what is available locally. So I did a stress and deflection analysis, using a 5000 lb distributed load on the bunks. It's just a quick approximation, I fixed the axles and let the tongue float.

I'm not trying to say these are the actual stresses and deflections, only want the trend. As expected, the bunks bow up and the I beams bow down and the tongue is down.

but it looks like the deflection will be much less if I just tie the bunks directly to the axles. You can only do this if you use torsion axles. Maybe just one extra bunk support to one of the axles? This is not why I want to use torsion axles, but maybe I can use much smaller I beams if I do this.

This trailer is the leaf spring design. The bunk ties to the cross members, not the axles, because they have to move up and down, but not with a torsion. Next step....finding out what size I beams I really need.

 

[Big Mike on Boats]

Talk to Tbevin here on BD. He built a great aluminum trailer and it looks like the best I've seen. You wouldn't believe it was built at home.
He built it for his 24 fb.

 

[K-Dogg]

Here is the original boat brochure, says the weight with engine (and stern drive I assume) is 3200 lb, and length is 20.5 inches and I just replaced the tank so I know it is 65 gallons.

So around 4000 lb with boat gear, ice, fuel.

View attachment 1485041

Top and side views
View attachment 1485042

Blackjack is pushing 5k pounds fully loaded with its 75 gallon tank. I’d imagine that an overbuilding and going w/ a trailer capable of holding 7.5k to 10k lbs would be ideal.