Thursday, March 22, 2012

Some thoughts on my next boat - a Demountable Monohull

These notes describe *some* of my thoughts that will drive the development of my next boat - a demountable monohull. I am calling it the DM12 but need to find a proper name soon.

The demountable monohull is inspired by "Phil Bolger's Breakdown Schooner" - featured in his book "Boats With an Open mind". Of course only the five remaining Bolger fans will have any idea what I am on about. This is not a big heavy fibreglass gin palace. More a lean mean contrary style cruiser.

Am thinking it will comprise 2 x 6 metre long hulls joined end to end - with a clever steel tube spaceframe that also forms the frame for the removable cockpit roof. Could even be 2 x 7.2 metre hulls or even something between these sizes if I can't fit everything in that I need.

So 12.0 to 14.4 metre length in total. Around 3.2 metres of beam. Around 1000 kg hull weight (~500kg each hull) using my ply/epoxy construction method - with another 1000kg of ballast and say 600 to 800 kg of rig and people things. No engine. Displacement of say 2600 to 2800 kg. Resulting in a CB up draft of around 340mm. But these numbers need to be developed a lot more before things are finalised.

It will be water ballasted (totally) - perhaps even 1000kg of water that autofills the lower hull - that part of the hull beneath the floor. This will be open to the surrounding water and will completely drain when the boat is hauled. Note to self: Need to model this properly using the hydrostatics software because the structure beneath the floor will contribute almost nothing to displacement. In effect it will be modelled like a flat bottom sharpie. The lower hull frames and walls just serve to keep the ballast water in place - all to make sure that inertia works effectively for us.

It is demountable because of winter storage and maintenance requirements and also to enable it to be built in the existing 12m x 9m facility - which is unable to accommodate a single 12 metre hull. This will result in two hulls built side by side and transported one by one to the nearby launch site. The trailer system will be simplified also because it only needs to haul ~500kg of hull at a time. The major transport challenge will be fitting the hulls into the 2.5metre width requirement - so they will be on edge. Note to self: Could possibly rethink the beam measurements?

Once at the launch site the hulls are floated off the trailer (one after the other as they are delivered) and then assembled adjacent to the shore. Should be an interesting sight for anyone observing!

Assembly involves placing and securing the structural spaceframe and tightening the bolts and nuts that hold it all together. Then assembling the rig, loading her up and sailing off into the sunset. Which will be an even more interesting sight!

The cockpit will be about 3 metres long - and be near the centre of the boat around the joint of the hulls. Perhaps extending equally into the rear and front hulls. The main centreboard will pass through this cockpit. Entry to each hull is via the cockpit.

There will be three daggerboards - front, mid and rear. Retrieved via a winch system. All to give some flexibility with managing pointing and rig balance. After all this is a bit of a radical prototype ;-)

Propulsion will be via two freestanding masts/sails/wings mounted ketch or schooner fashion - one on the front hull and one on the rear. Thinking about 50 to 60 square metres of Dacron across both masts - with CE down as low as practicable. Possibility of additional masts/sails/wings as the concept develops. Also will probably need a kite (as in wind sailing kite) for downwind work.

The image that I have in my head of this boat is that of Tom Perkins' 88m Maltese Falcon - major difference being that I don't have $270+ million to spend.

The front hull (looking forward from the cockpit) will contain the galley on one side and the shower/head on the other - adjacent to the forward cockpit entry point. Length about 2.4 metres each. Moving forward there will be a dinette / lounge that may also be converted to bunk space. This will be about 3 metres long. In front of this will be wet storage. Is that 6metres already?

The rear hull (looking aft from the cockpit) will contain the main lounge area about 3metres long - followed by the main cabin which is also about 3 metres long. Sounds about 6 metres to me.

All storage will be under seats and bunks etc. Need to find some hanging locker space - somewhere. Should be easy with all that internal volume.

Interior furnishings will be kept to a minimum and will also add structural capability to the hulls. The hulls will be built in the usual fashion - multi-chine ply with stringers and epoxy - sheathed in glass/kevlar. Each is a big monocoque - super strong and super light. 9mm Gaboon ply will probably dominate.

So that is my current thinking - let the development begin.

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