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Thread: Lapstrake planing hulls?

  1. #1
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    Default Lapstrake planing hulls?

    I'm thinking through a design for a small v-bottom utility skiff. I'd like to build it in plywood, and I'm thinking that if I build the bottom glued lap, I can give the boat a sharper forefoot than I can if I stick to bottom shapes that can be developed with large panels.

    So my question is what are some of the advantages and disadvantages of having laps below the chine? I know there are some planing boats out there with lapstrake bottoms. How come we don't see more of this? I'd think that the laps would act like little lifting strakes.

    Also, what is the thinking behind a reverse lap bottom, like on a Makenzie Cuttyhunk? I'm fascinated by those boats, but I've never understood the purpose of the reverse lap.

    Thanks for any insight.

  2. #2
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    Default Re: Lapstrake planing hulls?

    Reverse laps make good spray rails, especially if you include a batten in the land. If you get it right you will reduce wetted surface, and go faster.
    It really is quite difficult to build an ugly wooden boat.

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    Default Re: Lapstrake planing hulls?

    Reverse laps on a planing boat bottom makes sense and has been done over the years. To be most effective the layout can get a bit complicated as the strake width will likely vary a lot from bow to transom. The laps act like longitudinal steps and on a deep V there is quite a bit of transverse flow.
    Tom L

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    Default Re: Lapstrake planing hulls?

    The McKenzie Cuttyhunks are very pretty boats, but their construction is a bit funky (sawn frames, hard chine, lapstrake sides and reverse lap bottoms).
    Have you ever looked at the Jersey sea skiffs and all the variations of the Jersey shore? Traditional lapstrake construction of soft chines and steam bent ribs. Thousands of very capable boats from about 15 to 50 feet built over the course of almost a century. Many of them rather high performers.

    Historically I think you didn't see more because the Jersey shore was really the only area where lapstrake construction was the construction method of choice for a region. Most of the other builders of lapstrake boats built 'small' runabouts etc.

    While there may may be some 'advantages' in performance as you mention, however I think for the most part those differences are minimal in most situations. For example,.. Olsen's boat works in Keyport NJ built more than 200 boats from 16 to 42 feet. They started building about 1948 and in the mid 1960's changed from lapstrake to carvel construction (due to lumber availability). They built to the same lines and I can't say I ever heard comments about one construction handling differently than the other.

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    Default Re: Lapstrake planing hulls?

    Most every boat on the local lakes looked like this when I was a kid. I don't suspect that Lyman (here) or any of the others got too technical about the water flow and plank widths. These boats were relatively light and were simply given the power needed for the performance desired.

    -Dave

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    Default Re: Lapstrake planing hulls?

    Rifleman solves that problem another way -




    http://www.duckworksmagazine.com/02/...n/rifleman.htm
    "The enemies of reason have a certain blind look."
    Doctor Jacquin to Lieutenant D'Hubert, in Ridley Scott's first major film _The Duellists_.

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    Default Re: Lapstrake planing hulls?

    Thanks for all the quick replies. My mother's family is from the Jersey Shore, and I'm pretty familiar with the boats from that area. I've also spent some time looking at Lyman's. So is it safe to say that these boats were built with a lapstrake bottom mainly because the builders were familiar with lapstrake construction, and not because they were aware of some theoretical hydrodynamic advantage?

    Am I correct, that with all other things being equal (hull shape, power, conditions, etc.), reverse laps below the chine would provide a slight edge over traditional laps? Water breaks free at the lap, less wetted surface, therefore faster boat. But in a boat like the Lyman with traditional laps, wouldn't they provide a bit of extra lift? Or is it just added turbulence and drag?

    My final question: in a small boat without much power, does it even make that much of a difference? Say I built the boat with 3/8" plywood, I'm not talking about that big of a change from a smooth hull, anyway. It's not as if it's a Jersey Rumrunner with 1"+ planks and a big Detroit motor. Or do these little changes still make a big difference?

    I find all of this really fascinating. In the end, I'm just interested in any knowledge you guys might have the subject, regardless of whether it's applicable to my specific situation. Thanks again for your time.

  8. #8
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    Default Re: Lapstrake planing hulls?

    I have seen the results of running a powerboat model set up to record the direction of the flow on the bottom. It initially ran outboard forward, turning to flow aft under the stern. With the flow going outboard reverse lap will be a benefit, conventional lap will cause turbulence and impede the flow.
    It really is quite difficult to build an ugly wooden boat.

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    Default Re: Lapstrake planing hulls?

    Quote Originally Posted by OldDominionWB View Post
    Thanks for all the quick replies. My mother's family is from the Jersey Shore, and I'm pretty familiar with the boats from that area. I've also spent some time looking at Lyman's. So is it safe to say that these boats were built with a lapstrake bottom mainly because the builders were familiar with lapstrake construction, and not because they were aware of some theoretical hydrodynamic advantage?
    I would agree with you here, and in the case of the Jersey shore it is a result of what was developed in the early 1800's for light flexible boats that had to be launched off the beaches.

    Quote Originally Posted by OldDominionWB View Post
    Am I correct, that with all other things being equal (hull shape, power, conditions, etc.), reverse laps below the chine would provide a slight edge over traditional laps? Water breaks free at the lap, less wetted surface, therefore faster boat. But in a boat like the Lyman with traditional laps, wouldn't they provide a bit of extra lift? Or is it just added turbulence and drag?
    I have always sort of thought, or assumed that the extra lift generated by 'conventional' lapstrake construction would prove better than the idea of less wetted surface from a reverse lap. Either way I would be surprised if there were enough difference to notice any difference in the real world. (Maybe computer modeling could tell us the difference.)

    Quote Originally Posted by OldDominionWB View Post
    My final question: in a small boat without much power, does it even make that much of a difference? Say I built the boat with 3/8" plywood, I'm not talking about that big of a change from a smooth hull, anyway. It's not as if it's a Jersey Rumrunner with 1"+ planks and a big Detroit motor. Or do these little changes still make a big difference?
    I don't think you would see a measurable difference, but again that is just my opinion.

    Quote Originally Posted by OldDominionWB View Post
    I find all of this really fascinating. In the end, I'm just interested in any knowledge you guys might have the subject, regardless of whether it's applicable to my specific situation. Thanks again for your time.
    Here is a traditional lapstrake bottom at almost 100MPH.




  10. #10
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    Default Re: Lapstrake planing hulls?

    Ned, That top pic, looks like she is turning at 25 mph.
    What are the crazy fast ones, are they Jersey Skiffs as well?
    (racers from the 60's)

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    Default Re: Lapstrake planing hulls?

    Bruce, .... it may look like "Stubby" is doing only about 25, ........... However............. Stubby was built in 1949 to actually race against the unlimited hydroplanes of the time. She was built by Joe Clayton of West keansburg N.J.

    She was 30 ft long and powered by an Allison V-12 converted aircraft engine.

    One of these ---- this presumably is "the" engine, I have my doubts, definitely identical though.


    Here is Stubby being built in 1948.







    Subby was built for a guy named Jim Davis and his dad to race in the National Sweepstakes Regatta against the unlimited hydroplanes in 1949. Jim was the driver. Jim and his dad are pictured here.


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    Default Re: Lapstrake planing hulls?

    I believe Jim is still alive. I had a lengthy conversation with him about two years ago when he lent me these original pictures.

    This is Stubby when they were putting her in the water for trials.



    Jim told me that the picture I first posted above was at about 95 mph and she was running fine, and when he pushed her to about 100 mph she started to dip her nose (as in this picture).



    ......... and before he knew it she tripped and resulted in this.





    Jim and his brother (also aboard as the riding mechanic at the time) were ok. Stubby was recovered, rebuilt, and modified a bit.



    They missed the 1949 Sweepstakes Regatta, but made it to the 1950 (as I remember) regatta. The day of the trials at Red Bank N.J. Jim had Stubby out on the river putting her through her paces. He said she was handling ok until he opened her up to above 100 mph again, at which point the prop threw a blade right through the bottom of the boat (also right under him!). Jim took off his life preserver, stuffed it in the hole in the bottom of the boat and made it back to the pits.
    Stubby was again taken back to Clayton's shop in West Keansburg. This time however her (never really started) racing career was over. Her bottom was repaired, her engine was pulled (and reportedly sold to guy Lombardo for his famed "TEMPO IV" (G13), and she was rebuilt into an odd looking pleasure boat.




    ........................And yes, the crazy ones are "Jersey speed skiffs".

    This one was mine..... at about 65 mph.



    But they are really a flat bottom boat and are not lapstrake to the keel so to speak.
    Last edited by nedL; 03-01-2017 at 04:44 PM.

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    Default Re: Lapstrake planing hulls?

    Ok,...... and sorry about the drift here.

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    Default Re: Lapstrake planing hulls?

    For ideas about current up-to-date thinking, a lot can be learned from Graham Byrnes design info, obvious in the various plans info pages on his website.

    A really nice example, for a small skiff is his http://bandbyachtdesigns.com/jessy/ read what he has to say about Jesse's design - learn.

    And of course, his Woodenboat Design Contest winning http://bandbyachtdesigns.com/marissa/

    Cheers,

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    Default Re: Lapstrake planing hulls?

    Marissa looks eminently sensible.
    It really is quite difficult to build an ugly wooden boat.

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  16. #16
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    Default Re: Lapstrake planing hulls?

    Around here 15-17 feet long open planing lapstrake boats were built in great numbers in the 1970-ies and thereabout. They were by far the most common type of boat in my childhood in the 80-ies. Usually powered by a 20 hp outboard motor though some had only 15 hp and some had up to 30 hp.

    Fiberglass versions of those boats are built to this day. Retainling the lapstrake looking hull. Good boats.
    Amateur living on the western coast of Finland

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    Default Re: Lapstrake planing hulls?

    Fiberglass versions of those boats are built to this day. Retainling the lapstrake looking hull.
    The reason why the lapstrake "look" is retained is nothing to do with style. Its a simple way to stiffen the glass panel, creating rigidity. The same principle is also used with aluminium boats that are built from aluminium sheets that have a thickness of less than 2mm

    A really nice example, for a small skiff is his http://bandbyachtdesigns.com/jessy/ read what he has to say about Jesse's design - learn.
    Looks almost exactly the same as our Mushulu 12 design http://www.bowdidgemarinedesigns.com/MUSHULU_12.html





    Here's another M12 from another builder



    Here's one that was built in Canada

    Last edited by Mark Bowdidge; 03-06-2017 at 08:03 PM.

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    Default Re: Lapstrake planing hulls?

    We had an aluminum planing boat with lapstrake effects when I was growing up. My mother derisively called it the "Mayflower" because it's broadside of strake marks went so high for it's modest length. BTW I wonder if lapstrake-like bottoms aerate and reduce friction sometimes.

    Case in point... today I sailed a rubber dinghy quite fast with a longitudinally ribbed bottom (coarse corduroy pressure-cell pattern like lapstrakes). The wind was almost overpowering but smooth, and the wavelets were just tormented from short fetch. On a close reach I would hit the wavelets and spray really rapidly, and the boat almost seemed to run away frictionless (it is not supposed to plane, although I have with a wave crash against transom). It happened when I sat downwind side of it's modest V flat like a hovercraft.

    This didn't happen on any other point of sail. Close haul too slow, beam reach doesn't milk the wavelets, broad reach or downwind doesn't hit wavelets with enough relative speed.
    Last edited by rudderless; 04-20-2017 at 01:44 AM.

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