Converting sailboat to powerboat

The friendliest place on the web for anyone who enjoys boating.
If you have answers, please help by responding to the unanswered posts.
Heh. We've turned this thread on its head [emoji12]
 
Haha I know, right? It started talking about converting a sailboat to a trawler & now being discussed is adding sails to one! When I see steadying sails on a trawler, all I see is more work fiddling with lines. Plus, the deck space is compromised and we like the freedom of roaming the decks while underway.
I'm a fan of a true displacement trawler and their subsequent efficiency. A KK , Gulf Star or Schucker are always on my short list. I also prefer a single over twin but wouldn't take a Hatteras 42LRC off of the table, either. Our problem is draft. Our house on the Chesapeake is literally minutes away from the Bay and suits us fine for the time being but we're constrained by depth at the dock. It seems to me that a full displacement hull typically sits a little deeper in the water and we can't accomodate a draft of much more than 4' at our dock unless we want to plan departures and arrivals around the tide. It's a pain but the silver lining is we don't have to relocate in the event of a hurricane since it's very sheltered.
 
I'd think if you're going to the effort to add a small rig to most trawlers, you'd probably be better off adding paravanes instead.
 
A mast and boom can have several different uses. A nice paravane setup can actually be 2 masts and 2 booms if creative.
 
Physics
Keel and large rudder add wetted surface and parasitic drag. Sail boat hull won’t be as efficient as hull designed for power.
Remove part or all of above several detrimental effects. AVS decreases dramatically. Tracking becomes squirrelly. Tenderness and snap roll increases.
Even a minimal amount of weight 30 to 65’ away from meta center creates sufficient inertia to moderate roll and pitch. Loss of that weight creates uncomfortable situations even with small chop.
Sailboats swat under power. Bow rises, stern goes down efficiency and ride deteriorates. True for classic balanced hull with fine ends or slice of pizza hulls. Center of effort under sail is near midships and isn’t for power. Less of an issue if shaft(s) parallel to waterline but still present.
Sailboats( except when surfing) operate at or below hull speed. Not necessarily true for power.
So if you want an expensive way to get a poorly designed hull for power to operate at displacement speeds do a conversion. Otherwise get a hull designed for power.

There’s also a fair amount of powerboats with storm issues left in FLA. would go through those before considering a conversion. The above posts notes multiple visually satisfying conversations. However when compared to restorations of power boats with good bones there’s little question in my mind which is preferable.
 
I think the efficiency curves would depend on the speeds you want/need to travel.
 
Considering the fuel economy some sailors report when motoring, I'd think that as long as you stay a bit below hull speed (especially on narrow sterned sailboats that tend to squat badly under power) the sailboat hull will be more efficient than most (but not all) powerboat hulls. Especially if you cut the keel down a bit to reduce weight and wetted surface (stability won't be an issue, as once the rig is removed you can afford to shed some of the ballast).


Of course, the sailboat hull still comes with plenty of compromises as mentioned earlier in the thread.
 
I know for a fact my sailboats and my buddies 36 and 42 foot Catalinas and most other sailboats I have run blow the socks off similar sized powerboats if kept at their efficient speeds....maybe 1/2 or less mpg in decent weather... not sure what either set of numbers are punching to weather though.

Not saying the boats are similar in any other ways, just that some of those compromises involve hull shape that gives the sailboats the nod for slow speed efficiency.
 
On virtually every sailboat I’ve owned boat goes faster under sail than power and doesn’t squat. In light air that isn’t true but over around 10kts it is. Never understood not having the rags up unless it’s really calm.
Need to compare apples to apples. A Catalina 42 MK 2 displaces 20,500 lbs. A nordhavn 43 displaces 53,540 lbs. For FD hulls be they power or sail seems to me the comparison should by displacement. Not size if size means LOA. Doing this I think a sailboat hull will not be as efficient as a decent designed motor FD hull. Would you compare a Pogo or foiler to a full keeled heavy displacement sailing cruiser? Ones an ultralight in comparison to the other. This thread is talking about converting sail to power. Once converted the fair comparison is to a powerboat of the same displacement and range.
Think we need to avoid comparing a square back canoe’s gas consumption to a PWC.
BTW the ultra wide stern sailboats squat under power as well. It isn’t width of the stern but rather how quickly and how much reserve buoyancy comes in to play. These boat are typically ultralight and optimized to have the least wetted surface regardless of angle of heel. Sometimes more wetted surface flat than heeled. The past mantra “flat is fast” sometimes doesn’t apply. A hull designed with the propulsive force applied near the middle of its dynamic waterline even with a major portion of the forward vector coming from sheets will behave differently than one where that force is further aft. Also the propulsive force on a sailboat is applied above the waterline and power it’s below. Comparing an ultralight to a moderate displacement SD hull or a heavy FD hull isn’t a fair comparison. Displacements are vastly different. Comparing a SD hull capable of traveling 15-20kts to a FD isn’t fair either even at similar displacements. Rather compare two FD hulls power and sail of the same displacement. The efficacy benefit one would assume I think just aren’t there. Yes the sailing mega yachts are cheaper to run on passage under power. But that’s due to the expense of replacing soft sails and running rigging. Also they aren’t boats but small ships and the hydrodynamics are different. Efficiency doesn’t come in to it. From what I understand they aren’t more efficient than pure power mega yachts when under power either.
 
Last edited:
Doing this I think a sailboat hull will not be as efficient as a decent designed motor FD hull.


An optimized design for power use can certainly be more efficient than a sailboat hull. But especially within the budget of someone considering a sail -> power conversion, there aren't all that many powerboat hulls that meet that criteria. Willards maybe, but the majority of other powerboat hulls out there have sacrificed fuel efficiency for other things (such as ability to go faster, more interior space, ability to carry more weight, etc.)
 
sailboat to powerboat

Erle Stanley Gardner talks about converting a schooner to a power boat in his book "Gypsy Days on the Delta" seemed to work for him......
 
IMG_4758.jpg

I submit that there’s a stronger case for converting small sailboats to low hp (perhaps even electric) trawlers.

These pics are of my “Covid” project. I found a ‘new’ hull, molded in the 70’s for a 21’ sailboat. I built it from the gunwales up. Marine ply and epoxy added about 250 lbs above deck. Ditched the original inboard diesel, hung an 8 HP long shaft Yamaha, added 250 lbs of lead in the bilge, and ended up with a surprisingly roomy cabin. A fun reasonably easy project that can be done in your garage.

. IMG_0278.JPG
 
Excellent job V with an eye candy result. Have fun with her.

Others have been referencing a conversion for cruising. Returning to that subject. The Nordie 43 is 2.6 times heavier than the nearest sized Catalina and has a range of 2600 nm. To achieve the same range by adding tankage to the C would be absurd and weight would negatively impact on safety and performance. But do the mental exercise. Once you take any two FD hulls one optimized for power and one for sail and look at pound for pound efficiency under power guess it’s QED. Naval architects are smart folks. Now with the ultralight LDL power boats the deficiency deficit gets even worse. A Artnautica 58 with a 75-90hp engine gets 0.8l per nm or .21g/nm. At 14 tonnes (30864.72 lbs) it’s heavier than the Catalina 42 and with considerably more range (5000nm). Engine HP about the same as a midsized sailboat and a bit more internal usable interior volume than the Catalina. PS still think a boat designed to be efficient under power will be more efficient under power than a sailboat designed to sail. Pretty sure any sailboat hull under power is burning more than .21g/h at 7kts. Not just the C42. Maybe some multihulls come close but not monos with or without their keels. Friend had a Boreal 44. A light aluminum center boarder. A amazing strong sea boat but even with the board retracted although probably more efficient under power than my last boat or your friends Catalinas it’s nowhere as efficient as LDL power.
 
Last edited:
I agree most sailboats go faster with some sail in many conditions. Usually when they hoisted is where they quickly passed me in my trawler. Usually they were going nearly the same speed but burning 1/2 the fuel.

No, I don't have to compare displacements as that was never my point, and I clearly pointed out that same hull has its compromises.

Just saying motoring at slow speeds in many sailboats with or without a mast will burn far less fuel at low speeds than the vast majority of power.

Pretty sure, no...... absolutely sure of all my statements which did NOT include all sail hulls are more efficient than ALL power.
 
Last edited:
A large percentage of sailboat owners only sail in light to no wind, they like the idea of a sailboat but not the motion offshore. Most powerboaters do not leave protected waters.

Many sailboat builders recognize this and build modern sailboats with a large cabin and cockpit, shallow draft and the rig is an afterthought, therefor most modern sailboats do well in protected waters without their rig.

However, sailboats made to sail rather than made as condominiums do not do well because the GM (metacentric height) is designed with the weight of the rig in mind. Without their rig the roll is quick, snappy and uncomfortable.

The metacentric height (GM) is a measurement of the initial static stability of a floating body. It is calculated as the distance between the centre of gravity of a ship and its metacentre. A larger metacentric height implies greater initial stability against overturning. The metacentric height also influences the natural period of rolling of a hull, with very large metacentric heights being associated with shorter periods of roll which are uncomfortable for passengers. Hence, a sufficiently, but not excessively, high metacentric height is considered ideal for passenger ships.
 
What Antares said. The mast and rigging weight is offset by keel weight. The motion would be very uncomfortable. The hulls are also shaped differently for a reason. Used powerboats are more plentiful than sailboats. Buy one of those with a diesel engine, preferably without balsa cored decks. You're set to go.
 
Decent sailboats generally go faster with the engine off and sailing in any kind of decent wind. Many reasons but mostly due to increased immersion of the stern creating more turbulence, loss of laminar flow leaving the hull and increased drag. Over coming those effects requires more HP which many sailboats don’t have. I’m not talking motorsailng in light air but rather using the boat for what it was designed to do.
Will accept you were talking about your perception’s looking at the boats you see. Yes I was nitpicking. To my mind I’m not on a trawler but rather a recreational boat designed and powered to do 17kts. Trollers and trawlers are much more efficient than my SD hull doing displacement speeds. No getting around a boat designed to travel at a certain speed with a certain displacement at a certain length under power will be more efficient than a boat with those characteristics under power but designed to perform under sail.
 
OMG....a lot of book and little real world in my opinion..... and dancing around what simple real life people who power their sailboats all year round that sip fuel as long as they stay slow enough.

The original question was would buying a partially wrecked sailboat for cheap, work as a Carribean cruiser.

My wholehearted answer is yes.....probably.... if one does their homework on basic sailboat design and powering characteristics. Boats like old Morgan Out Islands can be a lot of fun with a quick homebuilt pilot house on them if gotten at the right price and people willing to live with all their other limitations. Lots of people have done similar and laughed all the way into the rum locker and Caribbean sunsets.

This discussion is a lot like people who think that all those Toyota Carollas in 3rd world places that cut the back roof off and turn them into pickup trucks should have gone out and bought 2023 Ford F-250s.
 
Last edited:
Rolling in a seaway, range, hull speed only. I can and has been done, wheelhouse, larger tanks, bilge keels.
 
And having actually been that liveaboard on my no-rig sailboat I say no way.
Unless it is a cat and there are plenty of those around after a named storm!
 
One boat/skipper experience doesn't make it a fact.
 
One boat/skipper experience doesn't make it a fact.
On the contrary, it is a fact. A fact for me, having first-hand experience.
Your opinions are exactly that, opinions. Nothing wrong with that.

I'm responding to the OP in hope that he looks for and finds the bargain
cruiser that's right for him with a bit of fore knowledge so he can be better informed.
 
Me too and I disagree that all sailboats perform to your opinion....thus not a fact but one opinion of one captain/one boat.

If facts were true to my opinion, it would be a scary world. That's why I dispute TF opinions that are presented as facts.
 
Last edited:
Ok here’s an opinion from from one who has been there done that backed by fact and experience. A dismasted sailboats would be a miserable boat in the Caribbean.
The North Atlantic gyre goes east to west from waters off North Africa to the Caribbean. Means bays on the west south west side of the islands are where you want to be. A cruiser will spend as near to 100% of the time anchored not in slips. Inspite of being in the Lee of the islands with some frequency there’s a north swell. It makes anchorages rolly. There’s generally a few spots in the northeast area of the bay protected from the north swell but they are filled first and people move into those spots as soon as they clear. The BVIs are an exception with quiet anchorages but very expensive, mostly mooring ball fields, lots of charterers, fewer places to anchor so avoided by cruisers.
As you go from island to island you commonly encounter compression zones. Often there’s wind wave from one direction and swell from another. It’s bumpy. There’s also areas between the mountains with significant downdrafts which can be bumpy as well. Given the wind is higher in those spots a non issue with the sails stabilizing the boat but miserable with no sail up.
So if you want to be miserable at anchor and miserable underway get a unmasted sailboat. If you want to be severely unpowered when trying to go upwind in tricky spots like the southern bays of Grenada get a unmasted sailboat. If you have any sense and want to stay married don’t.
 
De-masted sailboats do not make good powerboats even with modifications. The bigger the boat, the worse the conversion situation is. When most people think of seaworthiness, they think of ultimate stability and reason that a de-masted sailboat, will have the ultimate seaworthiness because it will right itself when rolled. That may be true but of little use as the "ultimate stability" boat will likely have severely injured or killed the occupants before they are rolled. Ultimate stability does little good if the occupants do not have the strength to hang onto a rail and are violently throw from one side of the boat to the other or are mentally incapacitated with the same result. The boat survives the storm but the occupants don't. These boats are often found floating serenely with no one on board. A de-masted sailboat must be modified to reduce roll rate if it is to venture where wind and waves are a given.
I am not saying that a converted sailboat will not be fit for purpose. I am quite certain that many sailboat designs can result in fair conversions. I am aware of designs that power better than they sail. Adding top hamper and a pilothouse can often bring an old sailboat hull within a reasonable roll rate for comfort. Many would be very suitable to doing the loop on a budget.
I would recommend doing such a conversion if the person has a burning desire to cruise, has no financial means of doing it otherwise and is pretty handy at cobbling things together. That person would need to have a big sense of adventure, be good natured, believe that hardship was very much a part of the adventure and comfortable with uncertainty.
The person converting the impaired sailboat would need to realize that no amount of dumping money into the project would net anything but a financial loss from the project and the persons time would be worthless in terms of money. Hull insurance would likely be unobtainable and liability insurance scarce.
The right personality would gain value from the adventure and accomplishment, especially if done for next to nothing in terms or money outlay. There are folks like this out there and their personality gains them favors everywhere they go.
Without that personality, you would face not only ridicule but certain eviction unless you are in very remote desolate locations.
A conversion should never be to replace an unaffordable dirt home situation. instead, you should posses a strong burning desire to adventure. The first situation will destroy you and the second situation will enrich you.
 
Quite a few people might argue as they have published their conversions and use....often very positive.

Many don't publish anything but still are out there, they just go out and do it and swap the travel stories at bars and marinas....which I have enjoyed.
 
Last edited:
"I don't recommend it to anyone."

That was an example of a conversion with specific intentions.

Buying a running junker requiring a tad of work to clean and make livable, to tool around in with no care about low initial cost and scrap it in a few years is a completely different story.

Only the OP know the "true" plan and intentions.
 
Back
Top Bottom