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Old 04-12-2014, 19:25   #1
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Doing The Unthinkable

Hi, I know this post will make some of you cringe, but I will ask it anyway.
Can a sail boat be used as a motor boat come cruiser if it has no mast or keel. I have bought a 32ft Miller/Whitworth yacht shell with a good reconditioned yanmar 20hp Diesel engine. But this yacht has no keel or mast and I have little funds to do a full refurbishment. So i am asking, would it travel through the water as just a displacement hull under engine power safely. Would it need some sort of ballast below the hull, but not the weight of the original keel. I am thinking it would, but can someone give me an estimate of how much weight it would need for stability. I have heard that diesel engines run under load for long periods usually have a longer life expectancy. So would this little Yanmar be able to cope with all day running in some circumstances and being raw water cooled too. I don't have the money for a big motor launch, but I could see this yacht with no sail giving me the ability to overnight and enjoy the coastal waterways here in Queensland, Australia. And as I said at the start of this thread, this boat used this way will probably get a few stares and mutterings from old salty sailors, but hey, the boat was destined to be scrapped in landfill so at least my idea will keep her alive. Your thoughts appreciated.

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Old 04-12-2014, 19:44   #2
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Re: Doing The Unthinkable.

The short is answer is no, don't try it. The boat needs the keel and the mast (dismasted sailboats have very twitchy motion.) When our 36 footer was dismasted, I had to hold the kettle down on the burner to make a cuppa. Without the mast's resistance to rolling, the gimballing couldn't keep up.


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Old 04-12-2014, 20:08   #3
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Re: Doing The Unthinkable.

I think the idea you have is alright but you obviously have have little understanding of boats. You might get away with it if it had the keel but not without both a mast and a keel. I have sailed on sail boats with the mast lashed on deck and i didn't note any peculiar motion, but I wouldn't go across a pond with both missing.

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Old 04-12-2014, 20:12   #4
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Re: Doing The Unthinkable.

Ann has a point but.... With much less weight in the keel (I think some external ballast will be needed) the motion may not be so bad. Also if your use will be only on protected waters like rivers or small lakes the motion issue may be moot. Many sail boats do a large portion of America's Great Loop every year and carry their masts on frames or ship them by truck for a good portion of it.

There is a lot to be said for an easily driven hull and a small diesel.

I would ask that question with specifics on intended use on one of the navel architect type forums like:
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Old 04-12-2014, 20:39   #5
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Re: Doing The Unthinkable.

You are going to need a keel to pull it down to its designed waterline otherwise it is going to be like a cork, but it does not need to be the same as the original design. I would do a longer thicker shallower keel of about the same weight. Without the mast you don't want the keel as deep as the original otherwise you will get that uncomfortable motion Ann talks about. The good news is you could probably do a Ferro cement and steel punching keel for short money if you are handy. Sailboat hulls with small diesels are very economical to operate compared to just about any powerboat of similar size.
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Old 04-12-2014, 20:57   #6
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Re: Doing The Unthinkable.

You can easily use the hull with no keel and no mast. but you do need Ballast. Most of the world's native peoples have ballasted sail boats and most of them from time to time run without sails, mast or keels. In Belize the native boats have very short keels because a lot of the water is only 2 or 3 ft. deep. I've seen them come into a harbor under sail with 3 yards of sand piled up in the boat with the gunnels about to go under water. They unload the sand and sail away with very little ballast, if it is not blowing very hard. Just don't attempt any long ocean passages. In the Bahamas when I was there a native had bought a 52 foot Morgan Out Island CC, with no rigging and him and his family lived on it and motored all around the Islands. with a keel and no mast the round bottom of the boat and the difference in water movement from the keel up to the surface will make the boat rock from side to side more than without the keel. Mac
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Old 05-12-2014, 01:24   #7
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Re: Doing The Unthinkable.

I go with Candy and Clockwork, it'll work but needs ballast. Internal should be OK, might be a little tender (might not). Since you already have the boat, do some tests at the dock (if it's in the water). You can use water itself as a test ballast to give you an idea; flood the boat to get it down to it's approximate water line, then calculate the weight of the water required. My guess is that about 40-50 80lb bags of concrete ought to about do the trick....
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Old 05-12-2014, 05:53   #8
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Re: Doing The Unthinkable.

In calm waters, it might be OK but in rough waters, most mono's will be very unstable, especially with no keel.

By the time you add a keel, you probably will be better off looking for anothe boat that already has a keel and mast (even if you just motor).
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Old 05-12-2014, 05:57   #9
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Re: Doing The Unthinkable.

You will get a pronounced rolling motion, if you can get some ballast low in the vessel it will slow the roll.
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Old 05-12-2014, 06:11   #10
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Re: Doing The Unthinkable.

The Ben Lexan designed boat?
Thats got really deep bilges, hasn't it? If you dont know, jump on board and pull the floor boards up and guage how much concrete in blocks, neatly shaped, you could fit.

My recollection is its a pretty light boat, anything Ben Lexan designed was meant to be light and f a s t (Just as the Americans lolololol). I reckon filling the bilges with concrete will do the job... Cost you bugger-all and only take a weekend. You'll have a nice displacement motor boat that will be very frugal on diesel.

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Old 05-12-2014, 06:26   #11
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Re: Doing The Unthinkable.

Bags of Quickrete should do the job very well and at little expense.
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Old 05-12-2014, 07:32   #12
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Re: Doing The Unthinkable.

Thanks, everyone for your advice although Candy did freak me out a little bit. I now realize this project is doable and will make plans for a home made long shallow keel as I am a welder. And steel punchings should do the trick, thanks Clockwork Orange. Just guessing the right amount of weight for the ballast will be the trick. And as more posts come in I might try the concrete in the bilges also, thanks MarkJ,(and I ejoyed reading your travelling posts). And on the subject of Bilges, why do boats have them, it seems to me to be a place where nasties can hide or rotten water to collect..... And just to stir the pot a little bit more, could I install a smaller, much cheaper mast forward of existing mounting point and have a twin head sail arrangement for down wind sailing when possible. And I will probably get the same advice, "buy the proper keel and mast" but money really is the issue as I am sort of a pensioner with very little means of earning much. The cost of a full size mast, rigging, sails and a proper keel is prohibitive, but I still want to enjoy the ocean. I am not a novice when it comes to boating and the ocean as I am a former surfer and have 30years of power boating experience behind me and I will only be coastal boating with most of it in Morton Bay Queensland (protected by Morton Island) and if possible a once a year holiday if the twin headsail idea can work sailing down wind with the last of our south westerlies that we get in our winters here going north and coming back home with the first of our northerlies in spring going south. I would be doing maybe 500klms round trip exploring the inside of Fraser Island and the southern most tip of the Great barrier Reef. As I said, just stirring the pot. Keep the advice coming.
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Old 05-12-2014, 07:59   #13
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Re: Doing The Unthinkable.

The real answer is going to depend on the shape of the hull and the use you put the boat to.

As mentioned, keels and masts add inertial mass to a boat that dampens its motion. However, the shape of a sailboat hull is dramatically different than that of a powerboat. Generally speaking, it is fact, the mathematically "optimal" cross section for a boat hull is a perfect circle as it provides maximum buoyancy and minimal wetted surface. But this hull shape also provides virtually no stability, whereas power boats, with their wider flatter bottoms and chines have built in stability. It's why a jonboat is dramatically more stable than a canoe.

Adding ballast of some sort will help add stability, but that hull is still going to be extremely tippy, relatively speaking. If I were in your shoes, I would find another hull, a powerboat hull, that I could use instead. Even if you start with an abandoned hull the work you'll put into it to make it usable will be less than the modifications you'll need to make to a sailboat hull, imho. Then there is the issue of the 20 hp. diesel. That is not a lot of power and is not going to power a boat larger than @ 25-30' with any sort of authority or safety.
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Old 05-12-2014, 08:38   #14
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Re: Doing The Unthinkable.

As all say, but as Suijin points out perfectly... That hull will ALWAYS be tippy/rolly without BOTH a mast and keel... Simply the wrong hull shape for what you want...

Given your propensity for tinkering, you could do what this guy did... but it didn't work out too well for him...

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Old 05-12-2014, 09:06   #15
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Re: Doing The Unthinkable.

Rather than a add a ton of dead weight that will just make the boat less efficient, you can add some amas and make it into a trimaran, or cheaper and easier use a single ama and thus like a proa or outrigger canoe.
Now it doesn't roll at all, like those sickening monohulls do.

And you can put in a nice cool trampoline between the ama and mainhull,
and have a place for the ladies to lounge (who will come flocking too visit your cool unique boat)

Or if you really want to make it simple and add the dead weight, don't make it dead, add a ton of lead-acid batteries and sell the diesel and convert the boat to electric drive, and the free boat might even be less than free, i.e. selling the diesel would more than pay for the batteries and drive.


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