Simple to build utilitarian outboard designs?

Discussion in 'Wooden Boat Building and Restoration' started by YotaTruck, Jun 18, 2013.

  1. YotaTruck
    Joined: Jun 2013
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    YotaTruck Junior Member

    I am looking to build my first boat and started out asking some questions in the main forum about pontoons and catamarans. I quickly learned that pontoons are highly inefficient (something of concern since I'm on a 9.9 lake) and that catamarans can be difficult to build for a beginner and that my weight requirements don't really match with the size I'd be looking for. That said, I've been looking into scows, garveys, and other utilitarian designs. Basically I'm looking for a boat to move people (4 including me) and camping gear across a two mile wide/2000 acre lake that does have a tendency to get quite choppy on a windy day. The shores of the lake range from soft sand to crumbled 3/4-1" granite, so the ability to be able to run the bow up on shore without more than cosmetic damage is desirable as well. I've found a few plans that I think might work well for the lake and that will also be perfectly doable in my garage with the tools and skills at my disposal. I have never built a boat, but I am a fairly experienced do it yourselfer who is a jack of all trades and master of none.

    The first is a Harold H. Payson/Phil Bolger plan, the 15' "Work Skiff":

    http://www.instantboats.com/instantboats_cake/boats/view/24

    What I like about this boat is that it's rated for 5-35HP. I have a 7.5HP outboard in good running condition, so I could use that motor for a while and see if it would be worth the cost to trade up to a 9.9 eventually. It is also a so-called "Instant Boat" design which doesn't require lofting or jig building, which I think would be a lot easier to tackle for a first project.

    Next is a design from D.N. Hylan-the 15'9 "Ben Garvey"

    http://www.dhylanboats.com/ben_garvey_plans.html

    I like the design but worry about the construction. I'm not sure that I want to take on a boat that requires lofting/jigs my first time out of the gate.

    Then there's the Phil Bolger 16'6 "Garvey Outboard Utility" which is kind of a mystery:

    http://hallman.org/bolger/isometrics#GarveyOutboardUtility

    I can't find a picture of it anywhere online, but it seems like something that would be right in line with what I'm looking for. I suppose I could contact the Bolger folks and see how much the plans are. If they're not that expensive I'll just order them to see what the boat looks like.

    Any feedback (or better suggestions) on either of these three designs based on what I want to do with the boat?
     
  2. MoePorter
    Joined: Nov 2012
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    MoePorter Junior Member

    Your general direction seems to be towards an underpowered sheet ply skiff & that's a good enough way to go but consider this direction as well -

    Given your existing engine & a possible "trade up to a 9.9 eventually" as your "big engine" along with your load & lake conditions I'd look into a 18ft -20ft -22 ft freighter canoe strip built. Strip building is well within your skill set & makes a light & beautiful boat much better suited to low HP outboards.


    Here's one example of the type -
    http://sandypointboatworks.com/boatstore/index.php?route=product/product&product_id=269
     
  3. upchurchmr
    Joined: Feb 2011
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    upchurchmr Senior Member

    I really like the freighter canoe over the Instant ugly boats.
    Just a personal bias, but I believe strip built can be reasonably quickly done if you work out a plan. It is much easier if you don't punish yourself to make it clear finish. Paint it and be happy.

    " I quickly learned that pontoons are highly inefficient" - I don't know what you have been smoking. There are always poor designs and those who don't know anything else.

    What do you mean by "highly inefficient" - If you are already set you don't need to answer the question.
     
  4. rwatson
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    rwatson Senior Member

    Pontoons are inefficient to build, and wasteful of materials. You get a lot less 'float' for the amount of material.

    You are essentially having to build a top deck on the two pontoons, plus all the connections to the living space, when in a catamaran, you at least get some storage as the cabin and deck extend up.

    Its bad enough having to build two hulls, without having the extra work of separate 'pods', and all the joining stuff to hold them onto the 'decking'

    Likewise, most pontoons are made of pre-shaped tubes, These create buoyancy issues the more they are submerged, as you get, as they get narrower in section when the waterline exceeds the widest point.

    Pontoons are OK when you need to dissemble the craft for storage perhaps, or you have been given free steel tubes, but it wouldn't be the starting point for a new build.
     
  5. upchurchmr
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    upchurchmr Senior Member

    OK I get it.
    The fact that most catamarans are much lighter that a monohull is probably immaterial
    The fact that they have less resistance when moving forward is probably immaterial
    If you are talking about party boat "pontoon" boats out of aluminum, you could be right about the waterline getting smaller as they submerge is a fact. Of course most people think you need some freeboard, which the upper half of the tube provides, while also providing the bending stiffness required to be out in the waves. Anyone who designs a boat to be loaded past the max width in the water deserves what he gets.

    When you design a boat ignoring all the basic needs of the material and the boat you will get something you don't want. :rolleyes:

    I have to agree with you completely.:rolleyes:

    On the other hand, lots of people talk about how square sectioned cat hulls are not very much increased resistance. Square crosssection is really pretty easy with plywood, or even strip planked, even when you taper the ends and put some rocker in the boat.

    Most catamarans that I would care to consider do have a weight limitation for their length. That may be the most realistic thing I've read and may well kill a cat being suitable.

    Who uses steel for a catamaran hull at 16' anyway? Must be some special requirement for ramming other boats.

    Yotatruck,

    A Tornado catamaran hull has about 2000# flotation at the waterline. you wouldn't press it that far so lets say 1000# with some freeboard. That is for each hull so you could get 2000# total. The Tornado is very seaworthy. I can turn you on to a guy who has 4 hulls, 4 crossbeams, 2 masts, etc for $800 OBO.

    Watson is right you will have to build a deck and that will take away from the payload.
    300# for the hulls and crossbeams (if you can use them), 800# for people (4*200# as an assumption), 400# of stuff, and that leaves 500# for deck and motor.
    Sorry but the boat is 20' long. I narrowed one from 10' to 8' so it will trailer with little problem.

    Probably a few issues, to me this would be a good start.

    Good luck.
     
  6. rwatson
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    rwatson Senior Member

    To continue, these are interesting points that can do with a chat I think.

    Cats may have 'less resistance', but you have to compare apples with apples.

    You need to talk about resistance with load carrying capacity. A well designed monohull will carry more load with less resistance than any two hulled craft.

    Small boats are always asked to carry more gear than they should, so its often a better decision to go monohull if you have fishing gear, people etc that need carrying.

    This is why smaller cats are mostly racing machines, especially the Tornado.

    But this usage also makes secondhand Tornado hulls and gear very cheap, as they lose their competitive edge long before they lose their seaworthiness.

    If you can get cheap secondhand hulls, I also think a useful work boat could be developed.

    Once again though, if you have to build from scratch, the monohull will provide a better carry to cash ratio.
     
  7. upchurchmr
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    upchurchmr Senior Member

    So hull speed is always an interesting thing for monohulls (little relevance for catamarans, unless they are too portly)

    I think hull speed =1.34 x square root of wl length.

    For 16 feet that = 1.34 x 4 =5.36 kts. This is the point at which you can't go faster without a huge increase in power, or starting to plane (which requires a large power to begin with).

    So at 5.36 kts you are stuck. Actually it basically happens before that.

    What is the "hull speed" of a cat? it doesn't matter, it doesn't apply.

    So If you only want to go 4 kts I agree with you Watson. But if you would rather be long gone get a cat.
    Now I will admit I don't know how fast a 7.5hp motor will go on an unknown catamaran. You will probably be limited by the pitch on the prop rather than power.

    Simple fact is that cats are more efficient from close to hull speed and above. So I have qualified my statement. I might even be wrong at 1-2 knots, but I don't much care.

    BTW, did you know that Tornados started as plywood boats? You can still get "plans" on the internet. I guess we would have to compare the exact material list with one of the 16 ft monohull box boats.

    Nice slam with the "tornado's lose their competitive edge" but what did that have to do with anything?
    Are you still going to compare a Steel catamaran to a plywood monohull? I guess that discussion got dropped, why?
     
  8. rwatson
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    rwatson Senior Member

    Yes, I know all about Tornadoes after having sailed them for many years.

    And yes, I knew they started as plywood - I had to repair one in Darwin after Cyclone Tracy damaged it.

    The reason all small cats 'lose their competitve edge" and you see them for sale only after 3 or 4 years ( and I have bought 4 in my time ) is that the extra weight from repairing dings, damaged gear ( rudders and daggerboards where applicable ) make it cheaper and easier ( and I suspect skipper phsychology plays a part in it ) to start from new.
     
  9. rwatson
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    rwatson Senior Member

    I dont think you still 'get' my point.

    Lets keep it simple.

    If you have two boats that have to carry the same cargo weight, a well designed monohull will require less material to build the hull and less power to push it to its hull speed.

    You will need to get over the image long skinny hull form of cats versus widebodied monhulls, that have it a higher hull speed. There are plenty of long skinny monohulls that have the same length ratio.

    I refer to the powered 30 ft long canoes of large river systems that can get over 30 knots from a 20hp outboard.

    Likewise - rowing shells, the epitome of hullform efficiency, are faster than multihull configuration where you make two smaller hulls large enough to support the rower.

    A real expert on the subject said
    "An optimum cat will require 40% more power than an optimum monohull for the same speed." Rick Willoughby
    http://www.boatdesign.net/forums/multihulls/multihull-ocean-rowing-vessel-26943.html



    I have never compared steel versus plywood ????? Where did you get that from ???
     
    Last edited: Jun 21, 2013
  10. upchurchmr
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    upchurchmr Senior Member

    Watson,

    "Pontoons are OK when you need to dissemble the craft for storage perhaps, or you have been given free steel tubes, but it wouldn't be the starting point for a new build." Were you not comparing using steel tubes to the plywood boats the OP suggested?

    Citing the boats Rick Willoughby is talking about is rather far from the OP's discussion, since they are very extreme, and human powered and don't apply. I have a great deal of respect for Rick and believe he is clearly right given his boats.

    Much as I liked MoePorter's suggestion of a freighter canoe, yet again you are not discussing something comparable to a 16' boat the OP suggested when you discuss a 30' freighter.

    I don't think a rowing shell could carry 4 people, a motor, and their equipment, in any acceptable form.

    Your discussion is to take some unrelated example and make an unrelated point, all while assuming limitations that probably would not be desirable. The OP might comment here. Seems obvious he is not interested, so I'll let you have any last comment you want.
     

  11. Easy Rider
    Joined: Oct 2009
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    Easy Rider Senior Member

    My freight canoe was only meant for 4hp but I run 6 and 8hp and get a wind in your face ride. Usually run near 1/2 throttle where the engine is fairly quiet.
     

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