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Thread: Realistic Displacement Figures

  1. #1
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    Default Realistic Displacement Figures

    I am buying a new anchor and trying to size it. Rocna will size the anchor based on boat length and displacement.

    Leketoy, a Roughwater 35, has a listed displacement of 11,500 pounds. I am assuming that the figure would be for the tanks about half full and nothing for any gear or people on the boat.

    How much should I factor up to get a realistic displacement figure?
    Elect a clown expect a circus

  2. #2
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    Default Re: Realistic Displacement Figures

    Quote Originally Posted by Bobcat View Post
    I am buying a new anchor and trying to size it. Rocna will size the anchor based on boat length and displacement.

    Leketoy, a Roughwater 35, has a listed displacement of 11,500 pounds. I am assuming that the figure would be for the tanks about half full and nothing for any gear or people on the boat.

    How much should I factor up to get a realistic displacement figure?
    What about windage? Seems length and displacement are pretty loose figures for sizing an anchor. As a comparison, Snoose is 36', almost the same length as Leketoy, but she displaces 28,000 lbs, more than twice yours. Yet I bet Snoose's windage is less than Leketoy. Most of Snoose is underwater while I'm guessing most of Leketoy is above water. Dunno. I kind of subscribe to the adage that no anchor is too big. I use a 45 lb CQR with about 50' of chain on a nylon rode. Worked fine so far, but maybe I haven't yet been in conditions to push it.

    BTW, next time you are hauled out, remember to ask the Travellift operator how much she weighs. They can simply read it out while she's in the air, but they usually don't bother unless you ask them to look.

  3. #3
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    Default Re: Realistic Displacement Figures

    Your points are well taken. At least Rocna factors in displacement; a lot of anchor manufacturer will give you a size based on length alone.
    Elect a clown expect a circus

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    Default Re: Realistic Displacement Figures

    Have you tried emailing the designer?
    I'll just take my chances with those salt water joys.

    AR

  5. #5
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    Default Re: Realistic Displacement Figures

    Quote Originally Posted by Bobcat View Post
    Leketoy, a Roughwater 35, has a listed displacement of 11,500 pounds. I am assuming that the figure would be for the tanks about half full and nothing for any gear or people on the boat.
    People sometimes define displacement differently, but standard displacement *includes* the weight of the crew and stores. Water and fuels tanks are typically assumed to be half-full.

    Displacement without crew and stores is usually called lightship weight.

    Kaa

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    Default Re: Realistic Displacement Figures

    Quote Originally Posted by Kaa View Post
    People sometimes define displacement differently, but standard displacement *includes* the weight of the crew and stores. Water and fuels tanks are typically assumed to be half-full.

    Displacement without crew and stores is usually called lightship weight.

    Kaa
    Good to know.
    Elect a clown expect a circus

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    Default Re: Realistic Displacement Figures

    I havre to say it also depends on your cable. I have only ever used all chain on my main and second anchors, the back up number 3 will still have a minimum 50ft of heavy chain and then a multi-platt warp.
    My take is its no good having a 60lb (insert favourite anchor) and then sticking a rope on it, when a 25lb anchor and all chain may hold just aswell. Just an observation, but when i was cruising many people would avoid dropping the hook next to a US flag boat,mainly because they used warp and had a overly large swinging circle.
    If you have a boat exceeding 11,000lbs, i see NO reason why you would not carry all chain as it dramitically increases holding power on an anchor. Forget anything made of aluminium except for a tender. Anchors are the best form of insurance, equip accordingly.

  8. #8
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    Default Re: Realistic Displacement Figures

    There is no standard for displacement, half-load might include crew or not, and at what weight each? It might include stores, but there's no standard....does it include the dinghy, or half the dinghy? What about the liferaft, spare anchor, cans of paint and tool box, holding tank contents, and the radar......and on and on......Don't believe any published numbers.

    For the RW35 I should think 15-16,000 pounds would be a reasonable place to start.
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    Default Re: Realistic Displacement Figures

    Quote Originally Posted by Captain Intrepid View Post
    Have you tried emailing the designer?
    Ed Monk Sr. has been dead for 40 years
    Elect a clown expect a circus

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    Default Re: Realistic Displacement Figures

    Quote Originally Posted by Bobcat View Post
    Ed Monk Sr. has been dead for 40 years
    I'll take that as a no then. :P A quick google did show there is still a manufacturer of the design. They're built in FRP, but the equipment/fuel/crew etc should be roughly the same weight no matter what the hull material.
    I'll just take my chances with those salt water joys.

    AR

  11. #11
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    Default Re: Realistic Displacement Figures

    Tad, thanks I think your figures are about right.

    Capt'n I if you found someone producing new Roughwater 35s I would be interested in the site
    Elect a clown expect a circus

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    Default Re: Realistic Displacement Figures

    Curses. Foiled by my quick and dirty google being too quick and dirty. Turns out its just an enthusiast's site, possibly where you got the 11500 lbs figure from.http://www.roughwater.com/default.as...t&v=35_36.html
    I'll just take my chances with those salt water joys.

    AR

  13. #13
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    Default Re: Realistic Displacement Figures

    Quote Originally Posted by skaraborgcraft View Post
    I havre to say it also depends on your cable. I have only ever used all chain on my main and second anchors, the back up number 3 will still have a minimum 50ft of heavy chain and then a multi-platt warp.
    My take is its no good having a 60lb (insert favourite anchor) and then sticking a rope on it, when a 25lb anchor and all chain may hold just aswell. Just an observation, but when i was cruising many people would avoid dropping the hook next to a US flag boat,mainly because they used warp and had a overly large swinging circle.
    If you have a boat exceeding 11,000lbs, i see NO reason why you would not carry all chain as it dramitically increases holding power on an anchor. Forget anything made of aluminium except for a tender. Anchors are the best form of insurance, equip accordingly.
    just for the record, I would probably prefer to have all chain, but that is $1,000 that is a little lower on the priorities list than a few other things right now. And for Puget Sound and the Gulf Islands the nylon rode with a length of chain is doing fine for now. But as we start venturing farther north, the chain will become more important.

  14. #14
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    Default Re: Realistic Displacement Figures

    Might note that for anchoring, the displacement is an indication of how much force can be applied to the ground tackle due to the buoyancy of the hull. Adding additional weight of cargo, etc., reduces the buoyancy, hence does not add to the stress on the anchor.

  15. #15
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    Default Re: Realistic Displacement Figures

    Bump for an old thread. I hauled the boat today and the travel lift scales showed a weight of !8,000 pounds. The old promo material for the FRP hull listed displacement of 14,000 pounds. I think Tad was right to bump it up a ton or so. I am not surprised at my boat's actual weight with a half load of fuel and a engine that is a bit heavier than the old (original Perkins)

    It will give me something to think about while I am scraping and painting bottom
    Elect a clown expect a circus

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