Mini Dashew FPB

Discussion in 'Boat Design' started by renko, Sep 3, 2010.

  1. renko
    Joined: Dec 2007
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    renko Junior Member

    while 2.5mm is actually reasonable for the level of safety and capability of the dashew FPB, is there a possibility to build something smaller and less sophisticated that still satisfies many of the build-goals as the fpb 64, namely, safety/ and efficiency over long passages.

    Obviously a fiberglass or similar cheaper alternative build will never be as capable as their build, but the concept is a great one, and seems that it could be scaled down to better suit the average wallat and usage. Weekend/week long passages etc.

    Or, rather than build from scratch, does it make more sense to take a 40' lobster boat and convert that? just some thoughts....
  2. CatBuilder

    CatBuilder Previous Member

    I would agree that you could scale the Dashew FPB down a bit (a complete redesign, but yet still sharing everything alike).

    I had looked into this as my perfect world cruising boat before we decided we were going to keep doing charters. We needed extra space for guests.

    I don't think you can convert a 40 Novi or lobster boat or anything, because it's a different hull shape entirely. The FPB is a very long, narrow beam displacement vessel and that's the secret to its fuel economy and speed. A Novi or other lobster boat is a semi-displacement type vessel powered to the hilt. Totally different hull shape from the FPB.

    They seem to rely on stabilizers... I'll let the experienced NAs here comment on if you could run the FPB without those active stabilizers.

    If you are doing weekend and week long trips (passages? crossing oceans? how far offshore are you talking?), you could definitely convert a lobster boat, which was also a hull consideration for us before we decided we were going global, rather than staying in the States.

    If you are talking about going up the Long Island Sound to Maine and down to FL and the bahamas, you can definitely convert a lobster boat into a very nice, fairly seaworthy liveaboard. IMO, it's the cheapest and fastest way to get yourself a nice, liveaboard vessel of that size.

    If you do go the Novi/lobster boat route, check in Nova Scotia. They have TONS of them for sale due to changes in fishing laws. Also, they have been lowering the number of lobstering permits in Maine and a lot of people are getting out of the business up there. You could find several good examples of boats to convert in those areas for a good price.
  3. apex1

    apex1 Guest

    I dare to disagree.

    The 64ft is already too small to fit the bill! Windhorse was the right size and speed. (both related)

    Going smaller perverts the idea behind these designs.

    And for sure a Lobsterboat of the mentioned size is nothing but a coastal cruiser (not all of them), never a boat for crossing oceans!

    what did you mean with 2,5mm ???

  4. Tad
    Joined: Mar 2002
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    Tad Boat Designer

    The reason no one crosses oceans in smaller boats is that it's no fun. Sailors don't mind (even enjoy) the rough stuff, but the vast majority of powerboats want comfort. I have a stock design for an ocean crossing 39' one's interested.


    Even though your boat is smaller, the waves remain the same size....thus motion in a smaller boat can get violent. A few years back two guys took a Willard (heavy displacement) 30' from Virgina to Bermuda at 4.5-5 knots. They could not believe how rough it was. And they had paravane stabilizers. The folks who ran a Nordhavn 40' around the world (publicity stunt) got fairly beat up at times, and it weighs about twice what PL 39 does.

    Dashews Windhorse is very small and light for her length, thus great ecconomy. A smaller version cold carry the fuel to do it, but that's about all.

    Typical Lobster boats are not intended for extended use offshore, modern ones are high-speed (18-20 knots) hulls....with very poor efficiency at lower speed.
  5. CatBuilder

    CatBuilder Previous Member

    Shows what I know about power boats! Nothing! ha ha ha

    Listen to the other guys above.

    In my post, I meant you could convert a lobster boat for inshore work. As to scaling down the FPB, where would it fail to work? I'm curious. As you got down to say, 40-50 feet, where would things become less desirable? (Attempting to learn by asking this question)
  6. apex1

    apex1 Guest

    As TAD mentioned, a really uncomfortable ride is one point. The loss of speed another one. But speed is required when the passage is long. You want to stay as long as possible in a weather system with moderate, to no winds (other than a sailor). Then, when the system changes to nasty conditions, you want to go out of the way. At least avoid the rough quadrant.

    That all means speed.

    Hence, longer is better.
  7. renko
    Joined: Dec 2007
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    renko Junior Member

    the 2.5mm number is US dollars to purchase one of the FPBs. Not a bad price if you are crossing oceans and living aboard. My offshore thoughts are 50 miles offshore, not 500. Definitely trips from Florida to Nova Scotia etc.

    The lobster boats we had in Portland (ME) harbor growing up mostly had huge engines. I suppose running them (or swapping out for smaller) at lower rpm would cut consumption, but as mentioned above, may not be the most efficient. Of course, the amount of money I would save on converting an older lobster boat could buy a lot of fuel (perhaps).
    Joined: Oct 2002
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    FAST FRED Senior Member

    Weather the hull of a "semi displacement" boat (lobster boat) operated at low speeds SL x 1.15 will be that much less efficient than a "true" displacement boat is a question of How Much?

    Few cruisers ever run at de-fueling speeds for hours at end (unlike the lobster guys with tax deductible fuel) so the low speed is the concern.

    IF the engine is optimized for high speed cruse (working lobster guy) it will stink at providing much efficiency at displacement speeds.

    Diesels love to WORK , and operating at 20% power is death.

    However a good used lobster boat purchased with a more rational engine , or re-powered with a displacement cruise in mind should work fine.

    Our current boat is a US Navy 50ft Utility with a DD 6-71 de powered with HC 55 injectors .3-1 gears 32x32 prop.

    At 7K the boat runs just under 3 gph, a tribute to the light weight (about 25,000lbs) and long LWL.

    Since 3gph on a DD is perhaps 45HP , purchasing a new re power engine of 75HP and keeping the tranny , prop and shafting would better the efficiency a bit.

    Never enough at our 200 hrs a year to pay , but a crapped engine could probably be replaced for less than a rebuild.

    Or a 6-71 swopped for a 3-71 , lots of options ???

    For deep ocean work the rounded bottom would give a smooth ride , but would require "flopper stoppers" to reduce the motion.

    The virtue of the Dashew boats is the long LWL so modest fuel burn can be maintained at a higher SL.

    IF this can (or should) be scaled down would depend on your desired comfort level.

  9. Pierre R
    Joined: May 2007
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    Pierre R Senior Member

    One thing to keep in mind about the scaled down FPB 64 from Dashew was that he kept the same beam as the FPB 83. With that in mind the shorter boat would be much more likely to resemble a boat with between a 3:1 and 4:1 length beam ratio.

    When I was playing with the numbers for a long skinny shallow draft passagemaker I concluded that you could not really get below 65 feet and carry enough fuel to make a faster passage. When you get below 65 feet you need enough beam to negate the long skinny shallow draft concept.

    George Buehler's Ildewild was only 55 feet with an 11 foot beam but needed to travel at low S/L ratios to cross oceans. If you are going to be down that low, what is the point in having a long slim passagemaker other than a few bucks in fuel.

    At a 9' to 11' (2.7M to 3.4M)beam its tough to have a really decent layout for the length. At 13' and up its much easier to have a decent layout.
  10. CatBuilder

    CatBuilder Previous Member

    Out of curiosity, what are your reasons for wanting to get out and cruise and get away from NYC? I once did the same thing you are... moved onto boats from NYC.
  11. renko
    Joined: Dec 2007
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    renko Junior Member

    Being transferred back to Boston, is allowing us (wife, 9 mo son, dog) a little more freedom to indulge in a boat. I like the FPB quite a lot, and actually think its a good buy for the capabilities you get, but in all honesty, dont think i can justify anything near that type of spend. Having said that, would like to think it is possible to take some of the concepts and apply them at a massively more affordable scale.

    I am not looking to cross an ocean, but certainly spend a week at sea. I have certain design criteria:

    My wife uses a wheelchair, but is very mobile otherwise. This is another issue with the narrow design. This is why i am drawn to the novi-eque lobster boat. Nice and wide, stable, seaworthy etc. Now, i may give up some range and efficiency - but i think i am willing to make that compromise.
  12. apex1

    apex1 Guest

    There are possibly solutions in sight.

    economical (though not to the extend of a FPB) rugged and a proven sea boat.

    even more economical (but a bit slower than the FPB)

    Both would allow easy boarding with a wheelchair and both allow for easy moving inside. Though the Malahide Trawler would need a custom made boarding gangway (pennies)

    It is important to recognize that vessel mass is a key factor in this case. For a given wave height, a heavy vessel will have lower accelerations or move less than a lighter weight vessel. That might be a ko factor with a person aboard not as capable of standing harsh conditions as you are.

    As with every vessel above some few meters (incl. the FPB) you would need a deckhand though.

    Both are very fair priced and represent a much higher value than the asking price.

    Give them a second view after noticeing they are both not what you had in mind!

    Transport to the US on own keel no problem and not expensive.

  13. Tad
    Joined: Mar 2002
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    Tad Boat Designer

    Most of the interior in a traditional raised pilothouse trawler yacht would be inaccessible to someone in a wheelchair. Therefor the conversion of something like this starts to make sense...

    Sell the 600 HP Lugger and the 2:1 gear and buy a new John Deere of 250-300 HP to turn the same diameter prop with a bigger reduction. You could build a huge cabin over the work deck and have almost all accommodation on one level, with perhaps a short ramp up to the helm area. Could be nice.....
  14. srimes
    Joined: Sep 2008
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    srimes Senior Member

    Are catamarans more comfortable for a given length? What would you consider the minimum comfortable size for crossing oceans in a cat? Just curious.

  15. CatBuilder

    CatBuilder Previous Member

    Thanks for sharing. I was just curious. I left (for full time work on the sea) after 9/11. After seeing that with my own 2 eyes, I figured all that office work just wasn't worth it. I used to keep a boat out in Long Island and take the LIRR out of Penn Station to go to it when I lived in NYC.

    Apex1 makes a very good point about the accelerations being more annoying for your wife than they will be for you. A lot of times, you need to stand up to deal with rough conditions. Since she will be seated, this will make her ride less comfortable and cause her to be more prone to seasickness. You will want to find a boat (as he said) with plenty of displacement (and the proper shape) to keep her from harsh accelerations that your bent knees soak up.

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