Affordable seaworthy cruiser

Discussion in 'Boat Design' started by goodwilltoall, Jul 31, 2010.

  1. MikeJohns
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    MikeJohns Senior Member

    The Dutch ones, they were designed by an English Naval Architect Charles Bentam, for the Dutch East India Company.
     
  2. Sailor Alan
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    Sailor Alan Senior Member

    All joking aside, I agree that you should endeavor to test your boat as Sam suggests. I have resorted to this several times in the past, indeed sometimes even sailing the boat before the interior was finished. Unless you can make arrangements to transport the boat back to the building site after this test, adding the interior later is made more difficult.

    I suggest NOT using people as ballast for this, they are naturally top heavy, and there is too much danger if the boat were to turn turtle unexpectedly. Using cement blocks, well lashed down, is good, but be aware lest they scratch or scuff the interior plywood.

    The way I see it, you have a couple of choices if your boat does not show an acceptable level,of stability.

    Adding ballast weight, up to a point, will add stability, though at the cost of fuel economy.

    Combined with the 3 masted rig you cartooned back a few pages, this may prove completely satisfactory. I would suggest a rig rather like the 'Spirit of Bermuda' shown here, though I would include short 'clubs' at each sail head, like a Dutch 'Botter' (I think), to emulate the Bermuda sloops of yesteryear. I would seriously explore using tapered aluminum flag poles as masts, probably using a deck stepped arrangement with NO stays. I would design and fabricate a base that had a flange just above the deck, held there by a welded steel structure picking up load from adjacent frames/bulkheads, deck, and hull. The flange, being just above deck, allows painting, and other access between the deck and flange. This hot dipped, and/or powder coated structure would allow people to walk through it I hope. These flagpoles have an aluminum or steel doubler inside them so the flange CAN take the full lateral load. The masts can be demounted for road transport, though unfortunately you might need a crane. The tallest mast need be only slightly longer than your overall length.

    Alternately, you could indeed add Arma's as suggested, making sure their shape is similar to the shape of the main hull, similar height, same bow rake, same flair, though clearly much shorter.

    http://img.nauticexpo.com/images_ne/photo-g/trimaran-express-cruiser-33511-7042763.jpg

    Something that looks a bit like this might be appropriate, clearly a power boat though. The three hulls need to be similar heights to allow easy integration as a whole, and not look 'tacked on'.

    I think trying to make it a sailing trimaran would require too much rebuilding of the original main hull, and be extremely difficult structurally.
     

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  3. Sailor Alan
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    Sailor Alan Senior Member

    Gentlemen,

    This might be off topic slightly, but I was wondering at the utility, or practicality, of this sail for GWTA.

    http://wharram.com/site/how-we-design/wharram-wingsail-rig

    I favor a rather traditional look for boats like this, and the low classic rig set on 3 masts is this in spades. Normally I would suggest a slight rake to the masts, with a classic loose footed, club headed sail, rather like traditional Bermudian Sloops. The above is a more or less modernized version of the traditional Dutch high aspect gaff rig, probably with vertical masts.

    Alternately, GWTA could use three of these sails, with a jib.
     

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  4. Emerson White
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    Location: Nordland, WA, USA

    Emerson White Junior Member

    So this thread hasn't budged in a long while, but if there is an update on what appeared to be a build underway I wouldn't mind seeing it.

    GWTA?
     
  5. goodwilltoall
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    goodwilltoall Senior Member

    Greetings,

    Hull was flipped a few weeks back n getting ready to build engine bed for hard mounting, before I do will insulate and warm up engine to hand start making sure it still runs "like new".

    Have a question regarding shaft and engine placement. As last drawing shows engine is placed at station 32 which is where I would like to keep it. This would require a new shaft of approx. 106". Now is this possible with the SABB drive line if using two (2) (have seen them called steady, babbitt and available from several marine dealers) bearings? For a 1.25 shaft have heard a max. unsupported length of 37.5" (x 30 shaft dia.).

    Hull CoB is at 27.25' however, with the keel its prolly close to station 32 (lost prior calculations). This brings up option #2 of using existing shaft cut at 41" with
    center of engine mounted at station 36. This would slightly change trim but most likely be ok but would prefer keeping as is.
     
  6. Emerson White
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    Emerson White Junior Member

    Awesome, been wondering if an update was going to come down the pike! I haven't got an answer for your questions but have you got a picture of your completed hull to share by any chance?
     
  7. goodwilltoall
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    goodwilltoall Senior Member

    Yes, maybe tmrw.

    Peace.
     
  8. Sailor Alan
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    Sailor Alan Senior Member

    Congratulations on flipping your hull, a major milestone.

    You are going to have to supply a side view of your engine instillation and propeller position so we can get a better idea of their relative positions, with some dimensions.

    Though you could support the center of a classic boat propeller shaft with a "Babbett" bearing, I would recommend against it. The boat itself flexes enough to cause this center 'babbet' to move laterally, and cause 'whorl' in the propeller shaft. All three propeller shaft bearings would also need to be 'self aligning' as well.

    I would strongly suggest making your fixed propeller shaft as short as practical, including your thrust bearing as close to the propeller as possible. Then use a simple automotive drive shaft, with a universal at each end, possibly from a wrecking yard for economy, to connect the engine to the boats propeller shaft.
     
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  9. goodwilltoall
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    goodwilltoall Senior Member

    Thankyou, yes I'll post drawings. Keeping shaft as short as possible is ideal but it would put engine further aft of which I calculated as doable but much better keeping closer to CoB.

    Keep in mind the SABB shaft it self turns and also moves
    fwd/aft (which I think is called movement along it's axial plane), discarding any ideas of using a universal joint.

    It's seems babbitt bearings are a long time accepted practice but just concerned about "axial" movement. The thrust bearing is located in the hub a few inches away from propeller so only two bearings are needed.
     
  10. goodwilltoall
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    goodwilltoall Senior Member

    Btw, a rough calculation puts actual CoB at station 28.5 almost exactly aligned with fuel tank. One reason would like to put engine there.

    Will give Sabb technical a call and hope language barrier can be easily overcome.
     
  11. Sailor Alan
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    Sailor Alan Senior Member

    On the contrary. Leave the engine where it should be for CG reasons. A proper car or truck drive shaft HAS a spline at one end and this is ideal for absorbing axial movement, in the boat hull, and/or the engine/gearbox. Actually, some universals DO have some axial movement, but not typically American ones.

    Make the solid propeller shaft as short as possible.
     
  12. goodwilltoall
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    goodwilltoall Senior Member

    CoG will be same either way but would have to do the numbers again because fuel, water, helm house move aft 24" and engine 50" otherwise have to put head in fwd cabin changing the layout I like. Maybe have pics this Aftnn.

    As the shaft turns Sabb designed it to also move fwd/aft along it length about 2", this changes the pitch allowing fwd/reverse while the engine shaft keeps spinning in same direction. Shaft is a threaded at prop hub and the push or pull of shaft turns a nut block for pitch control.

    So again I think this eliminates u joint idea. I would get a new shaft, fit/faced with standard couplers. No padded engine mounts, flexible couplers, self aligning bearings, etc. My understanding is this is done regularly on commercial boats for reliability. Boat is wood which absorbs vibration better than any other material plus there would be plenty more heft built into bedding.

    I know there would be some flex in hull but hope minor adjustment after its in water is all it needs.
     
  13. goodwilltoall
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    goodwilltoall Senior Member

    I know the babbitt bearings would work with typical engine and gearbox. Here are some pics.
     

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  14. goodwilltoall
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    goodwilltoall Senior Member

    Interior where I want engine
     

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  15. goodwilltoall
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    goodwilltoall Senior Member

    here go some drawings
     

    Attached Files:

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