What sort of trailer works best for a trimaran?

Reposting of this article is by kind permission of the author Mike Waters. A range of interesting articles can be found at his website www.smalltridesign.com.

Question: What type of trailer would you recommend for a trailerable trimaran and why?

To some extent, this depends on the ruggedness and weight of the boat being trailed. If it's of very heavy construction, then the typical stiff and rugged steel trailer can be made to fit. But it's more than likely your boat is lighter than normal and perhaps that the hull shell is also far more fragile than say, a typical motor boat. In such a case it's worth considering the options and what can be done to ease the burden while on wheels.

It's my belief that 'life on a trailer' for a fragile hull, can be tougher on its structure than anything the water can dish out or even the occasional grounding. The harshness of rollers and potholes can be brutal to local hull areas by comparison, and most trailers are also far too stiff.

Many trailers are built using standard trailer rollers and while these may permit the hull to launch and retrieve easily, are not the best for the light hull structure. Because the line of rollers cannot really follow the profile of the keel line, the boat will most likely be hauled with all its weight on not more than two rollers-perhaps even momentarily on one! That puts a huge load on one spot and there's a good chance that the hull bottom will deflect slightly to accommodate this load. Now, if you can imagine this deflection being swept back along the keel like a wave, you can see how easily it could cause internal delamination to the structure. Here's a trailer with this arrangement and it's far from ideal. Fortunately, this trailer also had very good torsion bar suspension, otherwise it might have been brutal on the road too.

A far better way to treat the sensitive bottom of a small and lightweight trimaran, is to use carpet-padded longitudinal hardwood runners (sometimes called bunk rails) under both the keel and perhaps along the bilge or, in some cases, up under the extended bridge deck, in order to stabilize the boat on the trailer. Multihulls general lack this transverse stability on a trailer and if not directly supported under the gunwales, usually get their on-trailer support from the amas that sit under the hull wings on each side. In the case of the folded Farrier, additional longitudinal runners are also run under the folded amas and these serve to share the load and stabilize the rig.

As far as suspension is concerned, almost regardless of trailer size, I personally like to see a trailer go down 1/3 of the total travel when it's loaded and if it's got a decent supple suspension that should be 1½-2". Use a yardstick to check this out sometime and you'll be surprised to see how many trailers are stiffer than that. I find this permits a nice easy motion on the boat with less shock than normal. You can generally shorten or slip out spring leaves to adjust this or even use lighter coils if that's the system used.

There's also the question of having a single or double axle. Like many things, there are pros and cons to both and neither one is clearly superior.

Personally, for light boats that absolutely do not require the extra load capacity potential of a four wheel trailer, I prefer a two wheel trailer as they are easier to maneuver and maintain. A four wheel trailer has to drag tires sideways when turning sharply - a two wheel trailer does not. But if using a two wheel trailer, I would recommend good tires and of large diameter -14 or 15" if possible, as they are far more durable than the smaller ones. This is particularly important for a two-wheeled trailer as if one tire fails, you are stuck. At least with four wheels, there's a good chance you can very slowly limp to next service station to get it fixed. Mind you, trailer tires are generally even tougher than standard car tires so in my experience seldom fail, unless allowed to really deteriorate with age and left uncovered for months in hot sun. I have also found that the four wheel trailers tend to resist up and down motion at the hitch. This might give a more level ride to the trailer but can also control the tow vehicle more and put more up and down load on the hitch. The two wheel trailer pivots more freely to suit road dips, though it's important to have at least 50-100 lbs load on the hitch when stationary. In fact I would suggest either 100 lbs or 10% of the total trailer + boat load, whichever is LESS. You need enough that the towing vehicles' rear wheels are always adequately loaded on the road but not enough that the towing vehicle's suspension is too depressed either, as that could reduce the grip of the front steering wheels.

As far as suspension is concerned, I personally prefer a transverse torsion bar system that can potentially at least, permit a larger wheel travel and therefore a softer ride. Mind you, everything has its limits and you don't want the whole rig wallowing around without some form of natural damping. Conventional shock absorbers tend to make the ride harsh though and unless proven absolutely necessary, I'd try without them.

Boats of 2000 lbs or more, will definitely be safer to tow on a trailer with an override brake. This system applies brakes to the trailer automatically, when the towing vehicle brakes, since the trailer then surges forward and the brakes are activated. Such trailer often has a handbrake for use when parked, though blocking the wheels is a safer bet in most cases.

For lighter sailboats (20 ft and under), I have built my own trailers from steel pipe or even from good, knot-free wood (BC fir normally). Both designs used a similar suspension system and this certainly gave a superior ride for the boat compared to the much stiffer trailers available as standard equipment. At the local scrap yard, I found the longest leaf spring that I could (40-50" long) with eyes of at least 1" diameter and had it burnt exactly in half. I'd use a truck spring for heavier loads and a long car spring for dinghies of say ± 200 lbs. I then used each half as a trailing cantilever spring and the fun part was that I was able to slide and remove spring leaves to get exactly the suspension support and movement that I wanted. A solid axle, machined for a snug fit within the spring eyes, worked well as an anti-roll bar and no other suspension damping was found necessary in my case.

While I see such a concept might be used up to say 1000 lbs total boat weight, I rather doubt it could go much higher and one would need to use a complete leaf spring each side with an unavoidably stiffer ride.

Details of the lighter, homebuilt designs could be available at a later date through this site.

Footnote:

"Obviously the chatter about 2 wheels or 4 concerns boats of 2000lbs or so. I'd use 2 wheels below 2000lbs total weight. Also, the mention of 14-16" wheel sizes, applies to such weights also. 12" wheels are fine for under 1000lbs. Although I personally love wood trailers for very light boats under 200 lbs, some States and Provinces have laws that do not permit this for highway use, so one needs to check with the local authorities".

"New articles, comments and references will be added periodically to my website as new questions are answered and other info comes in relative to this subject, so you're invited to visit and participate." -Mike

www.smalltridesign.com

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