Fast Launch 26

Discussion in 'Powerboats' started by Pericles, Jan 30, 2008.

  1. Pericles
    Joined: Sep 2006
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    Location: Heights of High Wycombe, not far from River Thames

    Pericles Senior Member

  2. Tad
    Joined: Mar 2002
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    Tad Boat Designer

    An "offshore capable" flat bottomed boat?

    No thanks.

    Tad
     
  3. eponodyne
    Joined: Aug 2007
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    eponodyne Senior Member

    Stretch it eight or ten feet, get the cruising speed in 4-foot seas to 22 kt (WFO in a flat calm to maybe 32 kt?), and maybe some vee in the bottom, and I'll start to be more interested. Pretty boat to be sure; but a pretty narrow set of operating parameters. I am, however, very impressed with Mr Mertens' creations, even if they're not entirely to my taste. He sure seems to do a workmanlike, thorough job with what he's selling.
     
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  4. Pericles
    Joined: Sep 2006
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    Location: Heights of High Wycombe, not far from River Thames

    Pericles Senior Member

    eponodyne,

    The FL26 is designed specifically in response to requests from his forum members. Jacques knows his marketplace. I'd love to build an electric version for use on the River Thames.

    http://forums.bateau2.com/viewtopic.php?t=14669&highlight=battery powered fl26

    I think you will be impressed with his TW34 when it's ready.

    http://forums.bateau2.com/viewtopic.php?t=11743&highlight=tw34

    http://forums.bateau2.com/viewtopic.php?t=11346&highlight=tw34

    Tad,

    The CX25 might have more appeal to you, but your Stahl 29 already is an excellent design.:D :D

    http://www.bateau.com/studyplans/CX25_study.htm?prod=CX25

    Best regards,

    Pericles
     
  5. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    I've had some success with relatively deep forefoot, flat bottom designs, but I don't think he'll get as comfortable a ride as he's hoping from this new design, particularly in broken water. Managed properly a well designed flat bottom boat can take open water, but few know how to handle a boat, flat bottom or not, in confused seas, so they're reputation grows out of the skipper's inabilities to drive in a seaway.
     
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  6. Pericles
    Joined: Sep 2006
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    Pericles Senior Member

    PAR,

    What time do you get up in the morning? You last post is timed at 4-25 AM in Florida.:D BTW do you have a website?

    Regards

    Pericles
     
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  7. tom28571
    Joined: Dec 2001
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    tom28571 Senior Member

    I know some who have success in open water in flat bottoms by trimming the stern up and the bow down. Still, I prefer a V because the same technique works even better there. There is loss of top speed because of a non-optimum trim angle giving greater skin resistance. It's a price I gladly pay on my boats.
     
  8. Pericles
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    Pericles Senior Member

  9. u4ea32
    Joined: Nov 2005
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    u4ea32 Senior Member

    Still seems like adding a V -- say 15 degree deadrise -- would transform the FL26 with just a few hours more labor.

    Neat boat other than the flat bottom.
     
  10. Pericles
    Joined: Sep 2006
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    Pericles Senior Member

    David,

    Choose another boat if you want a Vee bottom. The FL26 calculations are for the boat as it is. Jacques puts his good name and reputation behind his boats and unauthorised modifications change the legal position between designer and customer. The LB26 is the boat for you if everything else of the FL26 matches your needs. Compare the two.

    http://www.bateau.com/studyplans/LB26_study.htm?prod=LB26

    http://www.bateau.com/studyplans/FL26_study.htm?prod=FL26

    The Panga 28 and Abaco 23 are also coming along.

    http://www.bateau.com/

    Regards,

    Pericles
     
  11. charmc
    Joined: Jan 2007
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    charmc Senior Member

    Pericles,

    You make a very good point. The FL26 is designed along traditional lines, as an economical and easily driven hull, giving a reasonable cruising speed with less than half the power required to drive a hull whose V is carried to the transom. All designs are a compromise, this one appears to favor running economy while not completely sacrificing seakeeping ability. It is what it is, and changing the bottom would make it a different boat.

    For many years Pacemaker and Egg Harbor built rugged sport fishing boats designed to navigate the rough inlets of the New Jersey shore and the offshore fishing grounds of the North Atlantic. First in wood, then in fiberglass, the basic design used a deep, narrow entry which transitioned to a flat bottom aft. Even the latest fiberglass designs had only a few degrees of deadrise at the transom. These boats earned a reputation for being able to handle rough seas. I owned 3 over the years, including one of 26', and will testify personally to their excellent seakeeping capabilities.

    Moppie was developed to win races, and Dick Bertram began building deep V sport fishing boats for wealthy tournament fisherman who wanted to be first out and back and were willing to pay the cost. There's no question that a hull with a V bottom will go faster in rough seas, and ride well at those higher speeds. It's not that a boat like the FL26 will not ride well in rough seas compared to a V bottom design; just that the V bottom will enable higher speeds in those same seas if the owner is willing to pay the cost of more power and higher fuel consumption.

    The designer did say she's offshore capable, not that she's designed to be offshore most of the time. This design clearly is intended for operating mostly in sheltered waters.

    18 mph cruising speed in a 26' hull on 50 HP ... there's a market for that.
     
  12. Tad
    Joined: Mar 2002
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    Tad Boat Designer

    Please show me a 26' LWL, 3000 pound, 8' beam boat that requires over 100HP to manage 15.6 knots?

    The most important factors in any boat's performance and efficiency are length and weight; I say this over and over on this forum. Next most important factor is the engine/gearbox/propeller. Section shape is a minor factor. I would suggest that three hulls (flat, round, and vee bottom) of identical dimensions, weight, and power will run within a few mph of each other in dead flat water. Each form might have an edge at some particular speed.

    In 1958 Tom Gillmer ran a series of tank tests on light displacement fishing launches. He worked with four hull forms of between 29' and 34' LWL. One hull was a standard round-bottomed Maine lobster boat, next was deep vee lobsterboat (Bolger design) then a Chesapeake crabbing launch of very low deadrise (very similar to the subject of this thread). The final model was a Hooper Island boat of high deadrise forward with flat bottom aft. The round-bottomed Maine hull was the best, the hooper Island boat the worst, differences were on the order of .5-2 EHP at various speeds.

    These tests are published in Fishing Boats of The World, Volume 2.
     
  13. charmc
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    charmc Senior Member

    Scanning through a large number of tests, I found that most 3000 lb production boats had moderate to deep v hulls and hit that speed at between 2500 - 3000 rpm. HP ratings ranged from 150 - 225. Checking mfr's power curves, I found that 2500 rpm typically yields about 50% of peak power. That translates to at least 75 - 110 HP.

    No, this isn't the precision needed for an exact comparison, but it seems to indicate that the FL26, at 50 HP for similar performance, represents a significant advantage in operating costs.
     
  14. charmc
    Joined: Jan 2007
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    charmc Senior Member

    Tad,

    I took a look at your site and your Downeast 26 with a moderate V (15 deg deadrise). Interpolating from your published figures, I would estimate 60-70 HP at that speed. 20% heavier (3600 lbs), 20-40% more power, if I'm reasonably accurate.

    So the FL26 has some, but not nearly as much, of an efficiency advantage compared to your design. Maybe the answer is that most production boats are optimized for higher speeds, or just for easy production (constant deadrise).

    Overall, with the higher freeboard and bow flare, I would prefer to be in a Downeast 26 if I were spending much time offshore. And she's good looking, also.
     

  15. Tad
    Joined: Mar 2002
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    Tad Boat Designer

    Charlie, I wonder about the length (LWL) and beam of the 3000 pound boats you are using to compare. Realize that published figures are often wildly inaccurate, especially weight. What I've found is that there are few if any comparables. The Van de Stat Admirals Launch might be close but there's little performance info available. Some of the old Atkin designs are also close, but performance data is vague and questionable.

    So if we start from the basics of length, weight, and speed I find we have a speed length ratio of 3.05 and displacement/length of 76. A series of resistance curves I have indicate something between 60 and 80 pounds of displacement per hp will achieve the required 18mph. That puts power between 37 and 47BHP.

    Using Hatch's method I find a round bottom most efficient at this weight and speed, the round form requires 31.4BHP while the vee requires 35.7 for 18mph.

    Crouch's formula requires 30HP on the nose. And Keith's 39.3BHP.

    As always your mileage may vary!

    Tad
     
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