Sailboat into Displacement Powerboat

I have been contemplating converting a 30-40ft full keel monohull sailboat into a solar powered electric motorboat.
It would not go any faster than hull speed, like 6-7 knots.

I'm wondering if I should remove the lead keel. It isn't really needed without sails, but isn't the roll center going to change too much?
Some of its weight will be replaced with batteries.

The idea is to take a boat with bad motor and no sails or even rigging or mast perhaps, so this is an inexpensive little project.

 

Are you reinventing the wheel? When an auxiliary( motor powered) sailboat turns on its motor it is legally and in fact a motor boat. With rare exception a displacement type motor boat. When I go cruising in the summer east and west coast most sailboats are under power most of the time. There is little advantage except for low bridges for removing the mast or ballast and either may lead to bad unintended consequence.

 

NO Problem,,,

http://www.trawlersandtrawlering.com/wit/winniethepooh.html

 

You can shave part of the keel off, you need to leave some for the reason you mentioned. Go to the Rivers and Waterways of America, the guy advocates doing what you are thinking and there are links to other projects, one was a 46' or so, very nice job. I'd get a professional involved on the keel project as it is balanced to carry the mast and sail performance otherwise you'll be rocking away....

Ha, Fastfred got it!

 

Another example of how not to do it.....The guy spent $80k and 9000 man hours ($135k?) to create a boat worth $35k on the current market. Far better to just buy an existing Taiwan trawler for $45k......

 

I have a 30ft. Luger trawler that was sold in a sailboat, motor sailor, and trawler versions. Mine is powered by a Westerbeke W50, 41hp at 3200. cruises all day at 7kts. burning .5 gals. an hour. It's a comfortable and seaworthy boat that we enjoy. I don't see any reason that a similar boat couldn't be created out of one of the thousands of abandoned and neglected sailboats sitting around the country, limited only by your pocketbook, imagination and supply of elbow grease.

 

Another example of how not to do it.....The guy spent $80k and 9000 man hours ($135k?) to create a boat worth $35k on the current market. Far better to just buy an existing Taiwan trawler for $45k......

That may be true , but designing ,playing with the boat , building the boat , then using it is his HOBBY.

Its done HIS WAY, inside and out , no compromise with a marketing branch to make the boat sell quicker to Joe 6 Pack.

Most folks do not expect to make money from their hobbies .

He uses the boat as a calling card for his marine business , so there is some ongoing value.

That 30-40 year old Taiwan Tub may easily need an engine or two, as the Chinese composite (house ply with a layer of GRP ) deck and house structure are being replaced. At least an old sailboat is dry inside something that takes an old TT years to accomplish.

His latest project is a stripped 18ft boat with electric motor and batteries for canal cruising. Another money looser for sure , but its a HOBBY!!!!!

 

Yes, you can do it. I've made this conversion of a few occasions too. You can remove all or most of the appendages, but the ballast typically needs to remain in the boat, though possibly moved from a fin to the bilge. This is so the boat will still float on her lines.

Most sail to power conversions produce a boat that has much smaller accommodations, than a true power boat of similar displacement and they tend to be more Lively, particularly in roll.

For example, lets say you've found a hopeless Hunter 40, You remove the rig, build a light pilothouse and hack off the fin keel. The 4 tons of ballast is cut up into bricks and placed in the bilge, below the sole. You still have an 18,000 pound boat to propel with an electric motor. It would take a 30 KW electric motor to propel this boat with some authority and reserve capacity for windage, currents, etc. You could get by with a 20KW - 25KW, but you'd find occasions where this wasn't enough to make headway.

With this information in mind, do some simple calculations as to the battery bank, controllers, PV panels, etc. you'll need for this level of output. I think you'll find the PV panel deck space available wanting, unless you plan on also carrying a significant generator and fuel.

 

This boat will be mostly a test/demo boat for the solar-electric system I am developing.
In fact, I am planning on building a 40ft catamaran, but monohulls this size are everywhere.
The equipment (batteries and motors generator etc) can all be moved to a different boat.

So while I don't want to spend too much time and money on the boat itself, being an incessant engineer, I can't help but think I could turn one into a trimaran for more stability, and in fact put the electric motors in the floats/amas, similiar to the planetsolar boat but but as a trimaran, not a catamaran, and just in the back, like earthrace. Probably too much work.

planetsolar.org/wp-content/uploads/2013/06/IMG_0148.jpg

cache.gizmodo.com/assets/resources/2006/08/assboat001.jpg

 

Not "far better" if one wants a trawler that isn't overpowered and burn's only 1.5 gph. Most trawlers are just too barge like.
This guy did bite off too much re the "wreck".

But the result looks good.

 

I am going to go against the grain here and say that modern fat arse sailing boats hulls will do fine without the keel as ballast. Here is proof.

http://www.wavetrain.net/news-a-views/190-charter-boat-loses-keel-and-no-one-noticed

Someone hit a rock in a Jeanneau Sun Odyssey 37 and completely lost the keel. It took 3 charters and 150miles before anyone even noticed. Sure the stability would be dangerous under sail, but with no mast or sails it may well be fine under motor. These guys actually did sail the thing with no keel!

 

Nice story ....

 

Dennis, you'd be incorrect in this assumption. First of all, I don't believe the "skipper's" report on that Beni. He didn't notice anything different, because he was an inexperienced idiot and I don't believe he hoisted sail, as this would have quickly shown how far initial stability can be carried, missing over 30% of the boat's mass. Pleeease, she would have rode like a cork in a bathtub. This isn't that fat of a boat, with a 12' beam.

What I think is he continued motoring in, no sails, as the leverage in 12 knots of wind on a 45' tall rig and 12' beam boat is significant. Even the linked piece mentioned, asks "What's to learn from this absurd little fable?", so apparently the author didn't believe the story teller completely either.

I don't know the PPI on that particular Beni, but I can tell you subtracting over 2 tons from her mass is going to have a huge impact on her handling, particularity in 12 knots.

 

OK, so I was out at the boatyard yesterday checking on my cat hulls, and I hought..instead of converting a monohull, I can just use one of my 34ft catamaran hulls and make it into a trimaran. I only need one of them anyway to use as a male buck for female molds for the planned 40ft cat.

I will mock up my 1/10th scale model, and start a new thread on it.

 

Am I reading you right that you're considering making some huge changes to this boat's fundamental design and not doing any engineering to figure out if it's safe? Without sails and at low speed you'll obviously have a lot of reserve stability leaving the keel unaltered, but I wouldn't want to change the displacement and the CG so much without any analysis.

Similarly, I think a change as major as adding outriggers is perhaps a bigger deal than you're making it out to be. There aren't good rules-based loads for Earthrace-style training-wheels tris yet, so a lot of attention is required to ensure that the connections of the akas to the hulls, especially the main hull, are strong enough and have enough structure backing.

If you're looking at putting propulsion outboard, be careful to ensure you don't have submergence issues. Oftentimes really efficient designs have very little ama draft. Also be aware that putting more equipment in the amas can potentially increase the connection loads a lot.

If you want to start from an existing vessel, the main benefit is the fact that you don't spend a lot of money designing and building a boat. To take advantage of this, I recommend not looking at major modifications for this project. There are undoubtedly gains to be made by considering different, exciting hullforms but since you want something easy and cheap, you're probably best off changing nothing you don't have to.