Merging a Tamanu and a Hobie 18 again

Discussion in 'Multihulls' started by dstgean, Mar 24, 2010.

  1. dstgean
    Joined: Aug 2006
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    dstgean Senior Member

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    After the fun last year with my frankenhobie made of Gary Dierking Tamanu hulls and my Hobie 18, I've decided to build a second hull of my own (the first of the pair was my crew Brian's) to make a cat out of it. Like Ray's Slider, this will be a camp cruising machine with the intention of camping ashore unless conditions dictate anchoring out. Last time I reused virtually everything Hobie 18 including rudders, tramp, beams, mast, sails and stays. Overall beam was about 9'6" and was based on reusing the tramp.

    This next build will be a bit more focused on getting set up readily at some expense of stability. I want to go with a trailerable 8'6" platform with wings to add a bit of comfort and righting moment if needed. I'll be building beams after having cracked my H18 mast beam due to the independent hull movement upwind in a steep 2' chop. I may go with more than two beams to help counter that as well. I'm also thinking of going with a hard deck to make a nice flat 5' wide platform to camp on if needed.

    I do have a couple issues though. The first iteration worked well but the beam strength was a fatal flaw. Additionally, I copied the Hobie geometry to simplify setup and tuning. The Hobie roughly has 2' of bow in front of the bridle, 7' to the mast beam, 7' of tramp, and 2' aft of the rear beam to the stern & rudders. Adapting this to the Tamanu hull makes for some spacing issues as I built the decked version with 2 footwells. Copying the Hobie geometry placed the mast beam at the aft end of the front footwell--thus reducing the effectiveness of having a footwell at all. I did have nice helm balance, but after breaking the mast beam in the tramp track (luff groove) I moved the leeboard to the forward end of the cockpit to get the beast so balance under jib alone.
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    So, my questions are as follows:

    1. Would it be stupid to move the main beam foreward 1.5-2' to allow use of the forward cockpit? This would move the mast and sail plan forward as well leaving much less bow up there.
    2. What's the best way to deal with a hard deck that 5' wide while keeping it light?

    Thanks for the input.

    Dan
     
  2. dstgean
    Joined: Aug 2006
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    dstgean Senior Member

    Another thought is to put the mast aft by 18-20" and have the mast beam just in front of the aft cockpit. Then I could rig a tramp in front of the main beam.

    It seems that most modern cats have their masts well aft anyhow, so this would be a bit over 50% ratner than a bit under 50%.

    Dan
     
  3. bill broome
    Joined: Jul 2008
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    bill broome Senior Member

    a mast beam resting on the inner sheer log[ with some stiffeners ] looks like the easiest way to get the rig and crew stations portioned out. a 2 1/2 crossbeam solution.

    i was very interested in the use of lee boards. i want to move my dagger boards to the outside of the boat, but i thought a frame mounted on the sheer log and chine log would be easiest, perhaps just using one board. did you consider this?

    clearly you are having fun with this boat, in the water, and on the workbench. keep us informed.
     
  4. dstgean
    Joined: Aug 2006
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    dstgean Senior Member

    Interesting idea about the 2 & 1/2 beam solution. I had been thinking of some 1/2 beams for supporting a hard deck, but hadn't thought of a mast beam that would only land on one gunnel. I did hope to go with 3 beams anyhow to give the structure some added beef after having the Hobie beam crack in the tramp track/luff groove while going upwind in chop. Limiting that independent hull movement seems like a good idea. I really like the idea of the Hobie21SC and the Gcat with the front tramp. I'd realistically like to have a hard deck aft of the mast and a tramp foreward.

    Looking at the pictures of the setup used for the Texas 200 the big mistakes were trying to use the hobie beams for a boat wider that 8'. Teh decision that pushed the boat out to 9'+ was trying to use the H18 tramp while leaving the deck clear--thus pushing the boat wider. That's not a bad thing as I liked the stability, but meant the Hobie beam ends landed in the middle of the decks. I made a crude mould and had the combination of bolting and lashing the inboard end. Now I'd either bolt only or lash only. Either way, we had a fun trip, but didn't realize the potential of the boat as much of the time was under reduced sail for various reasons.

    I didn't think of using an outside mounted dagger board since I had my Ulua leeboard ready to use with one hole drilled--too simple to ignore. For the second iteration, I'll give it a thought as I never had trouble with the h18 and it's daggers two years ago. It would be simple and strong. i do like the thought of kick up foils though.

    Anyhow, thanks for responding, and I'll keep the group updated as I get moving along.

    Feel free to offer any further suggestions--especially on additional information about the 1/2 mast beam.

    Dan
     
  5. Chris Ostlind

    Chris Ostlind Previous Member

    Incorporate some properly engineered beams for the determined beam of the boat. Get used to the fact that they are going to be either fixed bolted for trailer beam requirements, or a part of a sliding, folding, system that gets you out to a wider, more stable beam.

    The Hobie beam stuff is to be trashed, unceremoniously, in favor of beams that fit the boat and fasten to all the hard points that offer the best, engineered points. Save the design of the mast step fitting and incorporate same in the new beam stepping point.

    Salvage all the sailing hardware and incorporate that stuff into the sailing solution that is needed for the modified boat. Run sail force vectors for the intended rig and mount the forward beam accordingly to take advantage of the best features of the existing hulls and their buoyancy characteristics. (do they really make sense for the rig being used?)

    Recognize that the boards (dagger and/or centerboards?) might need to be shuffled to reflect the different positions of the main/jib arrangement. Size the rudder to reflect the need for a foil that will not be compromised when the stern is lifted in certain sea states. Adjust the gudgeon and pintle needs to accomodate the larger, (if necessary) rudder foil and it's side loading. Adjust the trunks for the dagger/center boards to reflect the new mounting position of the rig, if appropriate.

    Consult with the boat/hull designer as needed to ensure that you have it all going on, before putting it out there in a tough environment.

    Test, test, test, the solution in various conditions before taking it out on the vast and salty where your radio becomes the solution to a less than solid design modification.

    Make use of offlist communication tools as needed.
     

  6. dstgean
    Joined: Aug 2006
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    dstgean Senior Member

    Incorporate some properly engineered beams for the determined beam of the boat. Get used to the fact that they are going to be either fixed bolted for trailer beam requirements, or a part of a sliding, folding, system that gets you out to a wider, more stable beam.

    >>Gary has given me the specs for just that. I'm going with 8'6" overall at present.

    The Hobie beam stuff is to be trashed, unceremoniously, in favor of beams that fit the boat and fasten to all the hard points that offer the best, engineered points. Save the design of the mast step fitting and incorporate same in the new beam stepping point.

    >>That's the plan sort of. I got a new main beam for the H18, and I'm keeping the H18 platform to share the rig. The sportier H18 can be rigged using the original mast & sails.

    Salvage all the sailing hardware and incorporate that stuff into the sailing solution that is needed for the modified boat.

    >>That's what we did for the last iteration, and it worked great short of having too weak of beams for the overall beam and buoyancy of the hulls.

    Run sail force vectors for the intended rig and mount the forward beam accordingly to take advantage of the best features of the existing hulls and their buoyancy characteristics. (do they really make sense for the rig being used?)

    >>The vectors are fine as they are transferred directly from one of the most proven designs ever built. The hulls are also amazing as used in this application considering the quick build and versatility. Could a better pair of cat specific hulls be designed for the purpose? Sure. But these are a huge stop up in comfort and carrying capacity from the H18. The only real bummer is the deck design puts the ideal mast beam location right at the foreward edge of the front cockpit. It would be nice to use that cockpit as a cockpit rather than a place to stow stuff --especially for daysailing.

    >>The wider beam boat is in many respects the better boat, but I'm looking for a quick launch time here. I suppose ideally I'd want a four panel hull witha v bottom foreward and flatter sections aft with a nice broad transom. I loved the concept of the J7 but assembly time put me off. Big volume hulls, box beams, transom hung rudders are all nice for beachcruisers.

    Recognize that the boards (dagger and/or centerboards?) might need to be shuffled to reflect the different positions of the main/jib arrangement. Size the rudder to reflect the need for a foil that will not be compromised when the stern is lifted in certain sea states. Adjust the gudgeon and pintle needs to accomodate the larger, (if necessary) rudder foil and it's side loading. Adjust the trunks for the dagger/center boards to reflect the new mounting position of the rig, if appropriate.

    >>I'll probably stick with the leeboard as it worked well both up and downwind in various sea states both upwind and down. Additionally, the adaptability of the Leeboard was nice when the weak Hobie beam cracked it's luff/tramp groove. I just drilled a new hole in the forward cockpit and ran under jib alone to keep the pressure off the compromised beam--with a nice easy helm upeind and down. I couldn't have done that with either centerboard or dagger...

    Consult with the boat/hull designer as needed to ensure that you have it all going on, before putting it out there in a tough environment.

    >>although I'm throwing it out here on the forum, I am indeed doing just that.

    Test, test, test, the solution in various conditions before taking it out on the vast and salty where your radio becomes the solution to a less than solid design modification.

    >>That's the goal! I'm looking for an expedition machine here, so solid and usable in all conditions I care to be out in is the mantra. At this point, I feel perfectly confident in the concept and the hulls as it really did work well in the T200. I just ran out of time and pressed the Hobie beams into a service they weren't designed for. With a bit more time, I'd have put together exactly what I'm planning right now. Beefy box beams, hard deck structure, reefable sail plan, wing seating, large volume hulls, and a front tramp.

    >>

    Make use of offlist communication tools as needed

    >>Thanks, will do.

    Dan
     
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