De-masted sail boat

[Hartleyg]

Originally Posted by Cargile

Thanks. I have heard/read that but to me it is counter intuitive. With the weight of a keel pulling the straight down I would think it would mitigate roll and keep the boat upright. Apparently not. Any further comment on why my intuition is wrong is welcomed.

I see several others have weighed in here


Here's what happens - when a keelboat has a mast installed, the boat rolls around the center of gravity. Because the mast & rig are long, their weight adds significant inertia to the rolling moment - that is, it resists change of direction, which slows the rolling and smooths it out.
When the mast is removed, the center of gravity goes downwards a little bit - but because almost ALL of the mass is only a few feet below that center, the rolling inertia is significantly smaller - causing the boat to roll rapidly, and with very quick reversals. The hydrodynamic resistance of the keel to rolling has surprisingly little to do with the motion.



Removing the weight of the keel, of course, solves the problem, so if you were thinking of converting a sailboat to a motorboat, find one where you can remove the weight of the keel!


Hartley
S/V Atsa

[Alden]

Originally Posted by Cargile

Any further comment on why my intuition is wrong is welcomed.

Try to keep your thinking about righting moment, rolling rate and angle of vanishing stability in separate baskets. The mass of a yacht's mast and rigging and its distance from the centre of gravity is helpful in terms of reducing the rolling rate, even though it is not helpful in terms of righting moment or AVS.


A boat which has lost its mast is more likely to turn-turtle in rough seas because energy from waves is more rapidly converted into rolling motion of the hull. If the mast is still in place, the duration of a wave's effect will not persist for long enough to tip a boat over far enough. The wave moves on and the boat returns to level.



When you were a kid you would sword-fight with broomsticks. Imagine how much harder and slower it would be to move the 'sword' if you taped a water bottle to its tip? As such, one of the best and easiest ways to reduce the likelihood of a sailboat being inverted by wave action is to add mass to the top of the mast. The reduced rolling rate helps the boat avoid being quickly tipped to the point of vanishing stability.

[svfinlandia]

Originally Posted by Montanan

The appearance of a boat as seen from off the boat loses significance once one gets on the boat. Pure aesthetics is mostly about vanity and little about function of form.

There are many "pretty" boats that one would not desire. A lot like persons.

The mast does significantly enhance roll motion and comfort and of course provides for motive force when equipped with sails.

Thus there is "beauty" when one sees the function of a form.

And that is why I love my motorsailer!

Al, S/V Finlandia

[SuW]

We heard from someone who was using a boat like ours (Bayfield 32 sailboat) to happily cruise the rivers, lakes and canals of North America.

They had constructed a solid handrail in place of the lifelines and also a large hard awning over the stern half, with solar panels. It looked decent.

Like many non-planing boats with small engines (in this case) it would have drawbacks - I wouldn't take it out in very bad weather - for example - but it would be a comfortable inshore cruiser.

[SuW]

I found a picture

[Cargile]

I do not want to "sail" at my age. Too much work and not fond of walking on the bulkhead. So a sailboat with sails furled and motoring would experience the same a unpleasant hull motion as a de-masted sailboat?

[rslifkin]

Originally Posted by Cargile

I do not want to "sail" at my age. Too much work and not fond of walking on the bulkhead. So a sailboat with sails furled and motoring would experience the same a unpleasant hull motion as a de-masted sailboat?

Not using the sails will generally lead to a less comfortable motion than sailing, but still having the weight of the mast up there helps a lot with avoiding violent snap rolls, etc.

Realistically though, if you have no desire to sail, there's no reason to buy a sailboat. There are so many powerboats out there to choose from that dealing with the downsides of motoring a sailboat around are likely not worthwhile.

[pbmaise]

Originally Posted by Cargile

I do not want to "sail" at my age. Too much work and not fond of walking on the bulkhead. So a sailboat with sails furled and motoring would experience the same a unpleasant hull motion as a de-masted sailboat?

No. I will try and explain it slightly differently.

Think about being on a teetertotter. With a very heavy kid on the other side, the kid on the light side will get thrown up into the air.

If you have two kids the same weight, there is no fast motion either direction.

That heavy kid is your keel. Adding a mast with sails...even if they are furled...helps produce a more pleasant hull motion.

[TeddyDiver]

To convert a sailboat to motorboat without masts you need to reconfigure keel also. You can't just remove it as the boat would float much higher and be unstable. Instead it needs a new shallow keel or internal ballast to be seaworthy and comfortable. For that to work needs some serious engineering calculations..

[ikebartlett]

Only one brand I would consider ( only because I haven’t come across any others like them) is the Gulfstar MS53 or its smaller version because Gulfstar used the same hull with the sailboat and the trawler. The cabin top and engine configurations were different. When out of the water the sailboat hull looks like many power boats and not like most sailboats. Less than 5’ draft,

[gulfislandfred]

I've had a couple of Morgan out Island 41s over the years. Shoal draft, long keel, fairly wide. I think they would make a good motor boat.


You can do all kinds of calculations, but it would be easier and more accurate to use some moveable ballast; water jugs, lead pigs, old brake drums, and make real world decisions. Start with similar weight to the rig you remove, and leave it more or less in place when you get it right. Secured, of course.


Lots of motor boats use short masts, stabilizers on poles that swing out, steadying sails, and other devices to combat roll.
I have known fishers who hoist a couple of 10 or twenty pound lead balls up into their rigging to slow the roll.

[Kettlewell]

IMHO, get a motorboat if you don't want a sailboat. The design will be optimized for its function. For one thing, why give up the potential for much shallower draft? Reducing your draft by a foot or two will double the number of places you can anchor here on the East Coast, and it will mean you can often find a nice quiet spot even in crowded harbors. Plus, typically powerboats have bigger fuel tanks for all that motoring you will be doing.

[captmikem]

I bought a Monk 38 motorsailor that the previous owner had removed the rig from. Totally, even the chain plates and tracks. I sailed it (motored it) from Seattle around Cape Flattery and down, across the Columbia River Bar and about half way up to Portland. Always a good swell out there, wind was light, 15 to 20 kts and maybe 6 to 8 ft swell. The boat did not roll excessively and it was pretty good trip. I really wish I had a mast for her though because I dislike relying on an engine offshore. It would have been a very pleasant sail. She is a good boat though and on the river here she is a fantastic boat.

M

[gulfislandfred]

Part of why many of us have a boat, is so we can do as we damn well please, regardless of the (perfectly reasonable) opinions of others.


I recently acquired a motor sailor, mostly because I like the way it's built, and it has a wheelhouse. Here in the Salish Sea, we probably motor, or motor sail, more than we sail, if we're trying to get somewhere, even in a boat that sails well in light airs.


My friend with an identical boat to mine (Fisher 30 ketch) has a pretty big Gennaker, which moves him nicely in light air.

[rossdv8]

Originally Posted by Cargile

You don't see many. There are many over the hill Motorsailers with ample living room and a decent engine but rarely do you see them de-masted. Aesthetics be damned. Thanks

I've had several and they were excellent motor boats, handled well in up to 3 metre waves and as long as the wind wasn't much above 30 knots and weren't all that rolly at anchor. If anything they rolled a lot less without the mast.

Now, the thing about them was - they were all 'small'. Two were 18 feet long, but yes, without the sails and a lot of other stuff aboard they had plenty of room for two people who liked each other, provided they only lived aboard for a few weeks at a time.

The others wer 26 foot and 24 foot respectively. They were like floating palaces by comparison. Plenty of roo to stand at the galley to cook, a decent double vee berth up the pointy end, and a wide single that comfortably slept 2 on one side, adn a narrow single that comfortably slept one and a half on the other side.

They were all Trailable, designed for racing and wild weather. The thing that made them comfortable that most motor boats don;t have, was that they were ballasted internally. One was an aging Hartley 18 that had somethig like 200kg of lead designed in each side of, and just ahead of, the centreboard case. Plus, when it was a yacht, it had a heavy 4 foot long by about a foot by about half inch thick cast steel centreboard.

The 26 footer had aboout 500kg of lead in the floor beside and behind the drop keel, plus about another 100kg in the bottom portion of the keel.
Both those were heavy enough not to roll too far, especially once they had 100kg of fuel and a similar amount of water down low.

While none of the boats would ever go close to planing, once they got mofing there wasn't much in the way of weather that stopped them. A bit of speed down the face of a wave, meant they had momoentum to power up the couple of metres high wave in front that was pretty normal here.

So basically - how well a boat designed specifically for sailing, works 'mastless' as a motor boat, depends a lot on what sort of sailing it was built 'for' and how it was built.

I only found this out because I was dismasted several times in cyclones and had to live with that for some time until the situation coould be rectified (money, money, money . .)