Sailboat to trawler / tug conversion

Discussion in 'Boat Design' started by cthippo, Jun 29, 2020.

  1. cthippo
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    cthippo Senior Member

    Not exactly sure where to put this, but since it is still in the dream phase and there is no conversions folder...

    I'm thinking about what I want to do for my next boat. The project I am currently working on is the nautical equivalent of a pickup, a utilitarian vessel that will comfortably seat two, four in a pinch, and carry some stuff from A to B. You could camp out of it and if you really had to sleep on board, but it's not ever going to be that comfortable.

    For my next boat I'm inclined to something more like a small RV, a vessel that will comfortably sleep 2 for up to a week and will go from A to B, but not in a hurry. Area of operations would be Puget Sound, southern inside passage, Columbia / Snake River system and perhaps California delta. I would prefer outboard propulsion to inboard, it needs to be trailerable, and not too large.

    So, looking at what is out there, it's not much. There are a lot of speedboats, some half assed powerboats with cuddy cabins and the helm in the middle of the cabin, and not much else. There are a few things I really like such as the Nordic or Ranger Tugs, but they are godawful expensive. On the other hand, there are lots of cool and innovative sailboat designs in this space, that are actually designed to be lived in, and do cool things with the space available to make that possible.

    And there is a limitless supply of cheap or even free 21' and 22' fiberglass sailboats out there.

    The obvious answer is to take one with a drop keel, secure the keel to keep it from dropping, recycle the mast, and enclose the helm position, possibly just adding sides and a rear to the pop-up hatch. The problem with this is that you still don't have a great helm position (Where you will be spending 6-10 hours a day), and the rear cabin is...sub-optimal.

    So, where I am going with all this is, has anyone seen an example of adding a forward cabin to a sailboat hull? Failing that, what are some cool, things you have seen done with sailboat to motor cruiser conversions?
     
  2. bajansailor
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    bajansailor Marine Surveyor

    CT, I am not too sure what you mean re 'adding a forward cabin to a sailboat hull'?

    I think that if you can get a small (say between 20' - 25') sailboat (preferably with a drop keel, and a transom hung rudder) for a give away price (or for free), then you could do a neat conversion on her.
    Taking a Cal 25 for example - ok, she has a fixed keel, but she has a large companionway hatch. Various other small sailboats have similar large hatches, often for 'pop tops'. You could maybe build a fixed 'pop top', and then add a small wheelhouse aft. Maybe even eliminate the cockpit, and have an aft cabin, with a deck above, perhaps with a hatch in the transom for access to the O/B motor from the aft cabin?
    Classifieds | CAL25 https://www.cal25.org/classifieds/

    This Swin Ranger is for sale in Britain, but is this similar to what you have in mind, minus the sailing rig?
    1981 Cox Swin Ranger 22 Cruiser for sale - YachtWorld https://www.yachtworld.com/boats/1981/cox-swin-ranger-22-3575956/
     
  3. brian eiland
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    brian eiland Senior Member

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  4. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    Be aware that the link for the designer (Mark Van) in Brian's link above is corrupted - I clicked on it and I got a Chinese site advertising (I think) women's lingerie.

    I googled Mark Van, and this appears to be his new site.
    Mark V Designs http://markvdesigns.tripod.com/boatbuilding/

    Paul Riccelli (who used to post as PAR on this forum - sadly he passed away a couple of years ago) also has some similar designs here -
    PARyachts: Riverboat series https://paryachts.blogspot.com/p/riverboat-series.html
     
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  5. Boat Design Net Moderator
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    Boat Design Net Moderator Moderator

    Good catch -- link should be fixed now.
     
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  6. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    Thank you Moderator for updating Mark Van's website link in the Gallery link posted by Brian.
     
  7. cthippo
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    cthippo Senior Member

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  8. tlouth7
    Joined: Jun 2013
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    tlouth7 Senior Member

    Any particular reason you want outboard propulsion?

    The biggest challenge I see is that you are going to affect the weight distribution considerably by removing the mast, and presumably increasing the size of engine hanging off the transom. Potentially the motion will be unpleasant without the inertia of a mast, though a lifting keel would reduce the stiffness somewhat.

    You could consider taking a fixed keel yacht, removing the keel and adding internal ballast forward. You could either fair the keel socket, or add a shallow keel to improve tracking.

    Then there is the issue that sailing yachts of this size are universally tiller steered. Given you are adding an outboard perhaps you could completely remove the original rudder, and install hydraulic steering of the motor. Otherwise you could possibly slave the tiller to the outboard steering mechanism.
     
  9. Will Gilmore
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    Will Gilmore Senior Member

    [​IMG]
    [​IMG]
    Yep, it's done.
    The first pic is a Mariner 19 conversion by a company in NC.

    I don't know about the second one except it's a sailboat hull.

    -Will (Dragonfly)
     
  10. cthippo
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    cthippo Senior Member

    I'm not sure that is a sailboat hull. I believe that is built as a double ended powerboat by All weather Boats in Ferndale WA. I don't know if they are still in business, but their sign has been out forever.
     
  11. KeithO
    Joined: Jul 2019
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    KeithO Senior Member

    cthippo, I also considered the outboard option, till I watched a few videos of it being done on calm water on a sailboat. I'm sorry but listening to an outboard thrashing along at 4000-5000rpm is just not for me when boat speed is just 5-6kt and one has to keep that up for hours and hours to get anywhere. On a planing boat going at 30-50mph, the wind blowing in your hair and waves slamming make you take less notice of how much noise the outboard makes.
    Example from YouTube

    I have a similar plan to you but mine is at a larger scale, 50ft +. This topic apparently does come up cyclicly on this forum and the threads are scattered all over the place. But the ballast and mast and associated righting moment are one of the hurdles to deal with. How to deal with it is a subject of much disagreement.

    Basically, once the mast is removed, or reduced substantially in size, the very low center of gravity due to the keel and the concentration of ballast there would make for uncomfortable motion, because the restoring moment is too great and the motions too quick. Some advice I found in this forum was that one would need to raise the center of gravity until the period of oscillation got long enough to be comfortable. In other words, take lead out the keel and spread it out in the bilge. It would have to be secured so that it would not shift when heeled, similar to what happened to the superyacht that rolled on its side and sank... At the same time one needs enough ballast to be sure she floats on her lines since merely removing the keel and sealing up the hull would produce excessive freeboard and very little stability at all. I think there have been a history of capsizes with McGregor sailboats that use water ballast instead of a keel and they can hardly stay right side up without their ballast.

    In my case, I'm not trying to gut out a sailboat and then graft on a pilothouse, I would want to keep the factory interior intact as much as possible to reduce the scope of the project. So that suggests a center cockpit donor sailboat would probably be best since I would just add a nice covered all weather helm over the cockpit and then figure out where to add the larger fuel tank in the interior. Of course remove a lot of sailing hardware since I wouldn't be needing it. I had found a 50' racing boat that was bare inside because they never installed an interior. Can work, but would take longer to finish. Positive is that it's sort of a clean slate and a lightweight high tech hull. So with a long waterline length offer good performance and economy perhaps 10kt at 4nm/gal.
     
    Last edited: Jun 30, 2020
  12. Will Gilmore
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    Will Gilmore Senior Member

    Lots of sailors drop sail in heavy weather and motor under bare poles. I have been at the helm under such conditions when a large wave broached over our 56' schooner with three 48' masts. She stayed perfectly upright while the wave rolled right over the top of us. I remember griping the helm, buried in water up to my armpits, looking out ahead and seeing nothing but water and two masts sticking up out of the sea. Then the wave moved past and we were still going. Not much in the way of heeling or rolling. The thing was, she had a 3/4 keel, 5 foot draft, a hard chine and a 12 foot beam. I was 13 and didn't know what she had for ballast. All these factors made for a boat that really liked to be upright. The weight and height of three aluminum masts and rigging could be, I'm just guessing here, a total 1200 pounds? That would put the center of mass for such a rig about 25 feet in the air. Would removing the masts and adding a deckhouse really change that much about the motion?

    We also ran 65 foot catamaran headboats out of Clearwater Marina. They moved with the waves much more and, at 25+ knots, could really give you a jarring ride.

    I guess what I'm saying is, I can't really see where the problem of too much righting moment is a bad thing.

    -Will (Dragonfly)
     
  13. KeithO
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    KeithO Senior Member

    I think the link between severity of sea-sickness and vertical acceleration has been well established.

    Any of the ships motions can result in a vertical motion, simply dependent on your position relative to the center of gravity. Eliminating the weight and windage of the mast and rigging removes a significant amount of damping which was originally applied to the vessel, even more when the sails are up... If you remove both mass and the damping associated with the position of that mass, then accelerations will go up, guaranteed outcome. Since the acceleration is caused by the weight of the keel and its large moment arm, and since one cant change the mass or the hull wont float right, the only option is to change the moment arm, by shortening it.

    upload_2020-6-30_23-27-57.png
     

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  14. brendan gardam
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    brendan gardam Senior Member

    we had a sailboat in a pen at our club with the mast removed for repairs. when the chop rolled through it bucked so much no one could board it. same boat with its mast fitted just rolled gently in the same sort of chop.
     

  15. Will Gilmore
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    Will Gilmore Senior Member

    How did that massless condition compare to a powerboat of similar size?
    I can see the logic of the dampening effects of a mast, but I don't see the inherent problems of hanging a weighted keel on a powerboat.

    -Will (Dragonfly)
     
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