Thanks DP, but that means I have to store a boat trailer in the summer and the tractor trailer in the winter, as well as have to pay to store my boat somewhere else than in the garage I'm building and I used that storage reason to sell the new garage to the wife.
Still not sure why a strong platform could not be attached to the boat trailer after removing the cradle, but I respect your experience, I just don't like it.:laughing:
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The issue with attaching a flat deck to a boat trailer is most boat trailer rails are not flat. I looked into this very hard back in 2003 when I was in need of a 18' car hauler type trailer. I could get a used boat trailer for very little but what was needed to modify it to haul a tractor safely would cost what a new car hauler would run me at the time through my connections in the trailer dealer business.
My marina will store a trailer for free as part of the dock or rack storage price. I assume this is what you have now. So that takes care of the trailer in the summer. During the winter the trailer will store your boat in your garage/barn you are building.
The trailers are really built so completely different that its just about a impossible task. A boat like yours at 4,200#'s and 22' long probably has 75% of the weight in the back 6' of the boat and the remainder forward of that point. Take a look at a picture of my small boat, a 25' Cuddy. The axles are set very far back and the structure in front of the axles is very minimal. This type of trailer converted would exert extreme tongue weight on your tow vehicle and would also need a lot of beefing up to handle the load forward of the axles.
This leaves you with one option, a car hauler with a cradle to haul the boat. I have done this. The question is how do you get the boat on and off. By the time you account for the "V" of the haul the boat will sit a few feet above the trailers deck and maybe 3' above the ground. Launching and retrieving the boat will be just about impossible due to the depth that you must back the tow vehicle in the drink. By the time you get it in that far it will try to float up. Been there done that. 4 tires and all that wood will float it for sure. Heck, one boat I deal with is 38' and has a purpose built tri-axle aluminum boat trailer with 6x6 bunks and it will float. Now you are left with sling loading the boat on the trailer. Do they have a boat lift of a crane with spreader bars and slings at your marina? How do they launch and retrieve it now? Do they use a marina universal trailer?
How do you get the load where you want it? Remember on a boat 75% of the weight is usually in the last 25% of the boat. This placed on a car haul type of trailer so that the outdrive can hang off the back will make for a very unstable tow due to axle placement. The axles are too far forward on this type of trailer. This will leave a very unstable load to tow and probably down right dangerous.
Now the next question is how do you get it off the trailer at home for winter storage so that you can use the trailer for other purposes?
The guys who's pontoon trailer we modified has a dock where he leaves the boat April15-Nov15 so he has use of the trailer all spring, summer, and fall for lawn chores but in the winter he is leaves the boat on it and is without a trailer. It has worked for him but he did borrow my 18' car hauler once to get retaining wall supplies.
Lots to think about.
Chris