Im going to start making my trailer today...2x7.6m of box section have arrived.
I looked at the profile of the hull and based the drawing/design around that.
Maybe worth a look at other boat trailers designed to carry the same style boat and go from there?
boat trailers are quite easy, if it has a keel then space rollers along the centre for the keel to run along then fit adjustable height tilting rollers to the outermost parts of the trailer to suit the boat.
i would think you would be better off building the boat then the trailer as you can build it to suit the boat but not the other way round
Thats exactly what I did when I was seeking inspiration for my boat trailer design...I found an indespension twin beam boat trailer at a local boat sales outlet which had the same sort of weight capacity as my trailer would need to have and I literally sketched all the detail parts and took measurements of everything I could...Later I went back and took photos, which helps a lot during the design process.
I didn't simply directly copy everything i sketched that day, I used my own design but I incorporated "styling cues" from various boat trailer designs including some from Extreme, DeGraff, Indespension, Nickleson and Brenderup etc...I tried to use the best parts from each to make a unique design that in some ways is better than all of them, and for the lowest possible cost.
Indespension dont use keels rollers so you have to reply on the support of their wobble rollers, but they simply don't use enough rolllers on their swingbeams to adequately support a boats hull and spread the point loads over a large enough area, in my opinion...Not a perfect design at all.
DeGraff use a lot more wobble rollers than indespension but they use horrible sky blue and grey rollers when I much prefer royal blue and white Bramber BR1 type rollers. Also when you consider how much they cost they actually look very cheaply made, almost bodged together in places in fact. They dont even bother to round off the sharp square edges to their components!
Extreme trailers offer lots of royal blue rollers on their swingbeams but I am not keen on their winch post design, even though its much tidier than DeGraffs.
I would say Nickleson trailers are marginly better looking than Extreme or perhaps about the same, but again they are let down by their winchpost design.
Brenderup use a beatifully elegant winchpost design and lots of brilliant engineering but they are let down by their use of keel rollers, which is like going back to the dark ages in my book!
So I am using a side rail design similar to DeGraff with Indespension design cues at the back but with my own design tweeks, DeGraff and Indespension swing beam design cues but with my own design tweeks, Indespension swing beam bracket design cues with my own tweeks, lots of Bramber BR1 5" wobble rollers along with some of their Welsh copies (you can buy them from "Turnsander" on ebay), Brenderup crossmember to side rail bracket design (but inverted and welded on the corners) and brenderup winchpost design cues but again with my own design tweeks.
I am still constructing it in fact and there is still a lot of welding left to do so I suppose I had better get on with it ....