[ Home | Contents | Search | Post | Reply | Next | Previous | Up ]
Validation_Box: third
From: Tom MacNaughton
Date: 01 Jan 2008
Time: 14:51:23 -0500
Remote Name: 66.252.37.136
Of course the first decision would be whether one wanted a sailboat or a power vessel. Either could be done very nicely. My wife and I have two boats with well under 8’ beam and as long as you can go longer to gain the accommodations you need there is not much wrong with a beam this narrow. It even has the advantage that you can keep the draft down and still get self-righting characteristics. Let’s examine a sailing version first. Let’s just arbitrarily say we’d go with a 33’ waterline. If you still wanted to be able to go offshore and not have to ship her everywhere you’d ideally have at least a 4’9” draft for really good downwind control in rough weather. This might result a boat that’s a little difficult to get into a shipping container because of your height requirements. However if you sacrifice some downwind control characteristics you could easily get the draft down to say a nice 3’9” draft with twin keels for easy shipping. With these proportions she’d still be able to go offshore in rough weather with one caveat. If you were running off in a bad storm you’d have to have a rig such as a yawl or schooner that you could balance for the conditions to relieve stress on the helmsman and you’d have to take the waves somewhat on the quarter so that if you lost control she’d roll rather than pitch pole. Nevertheless given that you intended to ship the boat whenever you could this would be quite a reasonable proposition. These days there are even self-propelled ship/drydocks specially built to carry yachts of just about any size and proportions. I’d probably resort to these, myself. Now let’s look at the case of the “Eventide” type canal barge. There is no question you could go a bit narrower than the 8’ beam shown in the Idea Designs section. Normally I’d build these out of steel or aluminum, but plywood is fine too. While you wouldn’t cross an ocean in these and would want to ship them there is no reason you can’t go across the English channel, given reasonable weather. To answer your other questions: If you just took the bow and the stern and put them together with no other accommodations between them you’d have about an 18’ boat which would make, say 5 knots with as little as 2-1/4 horsepower. That’s a speed to length ratio of 1.2. Now let’s go to the other extreme and take the longest vessel that will fit in the largest shipping container. In this case you’d have around a 39’ boat which would make about 7-1/3 knots, for the same speed to length ratio on about a 10-1/3 horsepower engine. Looked at another way it is getting hard to find a diesel rated at less than 10 horsepower. Also I think you can see that if, when you go up in length you don’t care if you increase the speed, the horsepower requirements would be even lower. All this assumes that you’ve geared down the engine properly to get a reasonably large propeller on there so you can pick your speed and pretty much go through anything. To add a section in the middle on a plywood vessel you should be able to cut the vessel carefully in two, move the ends apart enough to take the piece added in the middle and cut scarphs on all the cut ends. The new section has corresponding scarphs. Once everything is scarphed together the feather edges of the scarphs inside and out are glassed over to make sure you don’t get a stress concentration right on that feather edge. Done this way the longer vessel should be amply strong. Of course this presupposes that the scantlings were designed to be strong enough for the longest possible version. I hope that this helps.