Trail-able 'no-fold' Catamaran 7.5 x 3.6 coastal cruiser

First post ever...After much research and discussion, I have acad (and built scale model) a trailer design that will transport and launch a 7.5 x 3.6 bridge deck cat.
The many folding and de-mountable designs around are ok, but I would love a solid mini cruiser that could be transported to the water, launched and set up within 30 min, moored up for a season and then brought home to minimise ownership costs.
Whilst I have proven to myself that the simple design will work, I am not sure of the practicality of towing such a large load. The overall weight of boat and trailer will be no more then 3200Kgs and because the trailer itself will weigh more then the boat, (low centre of gravity) I expect the entire package to be reasonable stable. Towing dimensions will fit in the max allowable without extra permits of 4.3m high and 2.5 wide. Love some feed back.

 

We would love some drawings/details

 

I'm sure guzzis3 will be agog !

 

Are you planning on doing it like this? 6m wide. You have to check the road widths especially near the water as often trees are low and close together, never mind boats if launching in a boatyard. Or here, we took out 28ft x 14ft Skoota powercat 3000 miles from north of Seattle to Texas a couple of years ago (not many cruising boats go through the Rockies but ours did) Richard and Jetti's Cruising Log: Passing on the one http://woodsdesigns.blogspot.co.uk/2015/11/passing-on-one.html?view=magazine

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

This will give some clarity to the concept.

 

What kind of a side wind are you planning for during trailering?

 

You'll be using outboards?
So much stuff to take off the boat and then replace.

 

Not a fan of the approach. For one thing, boat would become a very unstable load on the trailer that way. You'd need to find the center of the load and then windage would be horrible. And the CofG would be far higher than a conventional trailering.

Make sure and empty the oil from the crankcases.

And the water from the water tanks.

And the toilet.

And the fuels.

And that map you left on the helm.

The Skoota I am building is a very large boat and I plan to get it on trailers, but it wouldn't gain a thing with this idea. The beam is 5M give or take.

I'd take Richard Wood's folding Skoota 24 design over that trailer every time. I might still build the Skoota 24 if Richard can put twin engines on it.

 

I agree with Fallguy's comments, and add in battery and anything left on shelves - galley stuff that should stay upright, lash down anchor?

Dan, glad to hear your Skoota 24 comment! Since drawing the Skoota 20 and 24 most outboard manufacturers have redesigned their 4stroke outboards so they can be tilted either direction. That means it is now feasible to have an outboard on each transom, yet still fold safely. I will be updating the drawings and my website as soon as time allows

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

Kurt Hughes has this design he uses a side tilt method to road trailer much like the off shore power boats do. Contact him perhaps. Kurt Hughes Multihull Design - Catamarans and Trimarans for Cruising and Charter - 52' Cruising catamaran http://www.multihulldesigns.com/designs_other/26cruisingcat.htm

 

The idea is ingenious if the actual loading and unloading can be accomplished easily and safely. If you are a short distance from a ramp, and it is a clear run without reverse cambers and overhead obstacles like low hanging tree limbs, it seems achievable. But if you have to traverse a railway crossing with electric overhead, I'd be worried. They've been known to arc on to high loads that aren't touching them.

 

Ha! Well here I am...

So here is my 2c.

Mr Woods has advocated several times carrying a cat at an angle, lets say 45 degrees. Turning it 90 degrees introduces a whole world of extra problems. As mentioned above you pretty much have to strip the boat of anything that can leak or move, and windage becomes a problem.

The height is manageable, you have to be careful of low clearances.

I am more than a little concerned about your 3200Kgs towing weight. A 25' boat should weight about a ton, 1000 kg. The trailer, even with the rotation, should come in about 500 kg. Adding weight to the trailer is a terrible way to stabilise the load.

I'm not clear on whether this boat is a power or sailing design. If it's power only why are you making it so wide ? yes you lose some efficiency but a narrower boat can be trailered more easily. Remember in queensland you can tow 2.9 meters wide with oversize signage, no permits or anything else required.

You might want to read the thread "modern hirondelle" that I started a while back. It focuses on a 7 meter long 2.9 meter high bridgedeck sailing cat. I was quite surprised to find I could fit a proper queen bed 2 decent singles a dinette galley and enclosed heads/shower with standing headroom in the hulls into that compact package. It won't be spacious.

The boat is loaded onto a conventional catamaran trailer that supports the boat under the bridgedeck. The hulls are partly outboard of the wheels and depth to launch is not unreasonable.

Also that boat will take a 4hp outboard, removing the NEED for registration ($345/yr in qld). It should do close to 6 knots.

You really have to start with a criteria, what accommodations and payload do you want ? where are you going to take it ? how long are you prepared to spend assembling and breaking it down/launching, how many people to help...and of course how much are you willing to spend to build it. It's good to have ideas but if you are going to implement them you need to consider use.

 

It's about 3 meters in queensland for train overhead if I remember correctly. Within 3 meters you can get it jumping, and if it does it'll destroy anything in the current path. If it's you you may survive but you'll wish you haddn't.

 

It is a real engineering challenge to get the loading and tilting mechanism to work reliably and safely, imo. For all requirements to be met, apart from the normal requirements of new trailers, may require special compliance certification for the tilt mechanism, I would be talking to the Transport Dept about that, or a trailer manufacturer before planning too far ahead. There is no way the trailer will come in under a tonne, with all the ironmongery involved, and it will need full breakaway braking, and the total kept within 3.5 tonnes or require a out-sized tow vehicle (truck).

 

Another problem I can guarantee is bearings will fret under loading like that shown. The bearings would need to be removed from the equation while traveling or bearing wear from bumps on the road is certain, so you'd need to remove the bearings somehow after the turn.

I know because I am considering linear bearing launch arms and they will work, but not under load while traveling; same problem. Sorry if I'm shooting holes, but better than spending 5 grand on a trailer turning apparatus only to have bearings fret after the first 500 miles and require new bearings every 500 miles.