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Old 14 August 2010, 07:19   #1
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RNLI DoDo trailers

I need to design and build a trailer for a 4.7m sib suitable for beach launching and I'm looking at doing something similar to the DoDo (Drive on/Drive off) trailers, ie pointing the boat the other way.

Is there any D-class crew etc on here with experience of this type of launch/recovery? Or anyone else who has done something similar?

Any advantages/disadvantages? How likely are you to hit the prop/leg on the way out?

Also any pics showing how the trailer's put together would be really useful.

Another point I need to look into is how to support the boat properly. This one's got speed tubes so I'm guessing you don't want a flat trailer bed which would squash the speed tubes? Would I need to shape the trailer beds so it supports the main bouyancy tube without interfering with the speed tube?

Any help/suggestions/photos/experiences all gratefully received
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Old 14 August 2010, 08:10   #2
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How 'bout fitting wheels and hitch to a pile of aqua-dock?
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Old 14 August 2010, 09:13   #3
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The D class trailer is U-shaped (supporting the tubes from underneath, and joined at the tow-bar end, where the engine end up) and has high bars on either side which keeps the boat square on the trailer - so it's quite difficult to hit the leg whilst recovering (not to say it can't be done - but not managed it yet). Also, the leg is usually tilted up during recovery anyway.

On most D class DODO trailers, the tubes sit on rollers set into the flat surface of the trailer - but the underside of the tubes can still sometimes get damaged. There are several different designs, with differing number of rollers. I think the general view is the more rollers the better...

It will be fine if you are launching off a slipway - but difficult on a beach. On the beach, the tractor has to go deeper than you'd (probably) take your car - there is no winch so the boat has to be pushed/floated/wrestled on - much easier with some waves!! - but difficult unless theres a few of you.

The D-Class recovery looks easy, but there are at least three crew to move it about, a tractor driver that knows what he's doing (who can tilt/raise the trailer using the hydraulics on the tractor), so whilst it's not difficult, it not as simple as it might look!!
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Old 14 August 2010, 09:21   #4
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Quote:
Originally Posted by Mollers View Post
How 'bout fitting wheels and hitch to a pile of aqua-dock?
Genius, Nauti Buoy will have that pearl of wisdom copywrited 1st thing monday

Small edit: Further research shows that the speed tubes are under the floor rather than under the main tubes so they shouldn't interfere with any trailer bunk arrangement from what I can see?
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Old 14 August 2010, 09:38   #5
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Thanks DGR, I found a pic of the trailer you're talking about which I'm using as a starting point but it doesn't show much detail.

I didn't think rollers would be necessary given the weight of a sib, I was thinking of making GRP mouldings to match the underside of the boat. I've done this before years ago with a beach launching trailer I made for an Orkney Fastliner. Priority for me is supporting the boat so if I used rollers then yes, I'd want an awful lot of them but cost and maintenance, I'd rather not. Bad idea?

Beaches are generally very flat here, too much for a non-submersible tow vehicle so the indian rope trick would have to be employed. Therefore I don't see a problem with just getting the trailer a bit further in and floating the boat on, like you say with tall sides on the trailer to locate the boat in the right position.

Is that 2 buffers in the pic below that touch the cones to prevent the boat going on too far?
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Old 14 August 2010, 11:57   #6
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No - the bumpers stop the boat when it comes onto the trailer - and the transom sits against them, and the engine goes in between them. I've taken a photo - but haven't got anything to reduce the size of the image on this computer......

Ahh - there you go. Hopefully that's better? The tubes sit on the flat bits with rollers, and the bars that go out towards the middle support the hull membrane (uninflated). The nose of the boat is pretty much unsupported.
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Old 15 August 2010, 17:12   #7
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I'm missing something here, what's stopping you Do-Do-ing on a normal trailer?

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Old 15 August 2010, 17:49   #8
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Bits of metal in the middle of the trailer that'll make a mess of the bottom half of your engine
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Old 15 August 2010, 18:40   #9
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Not if you drive it on forwards, like you're meant to If it makes a mess of your skeg then you've knocked the bow post over! TOO much throttle!

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