Low power boats

Discussion in 'Boat Design' started by wavepropulsion, Aug 4, 2013.

  1. wavepropulsion
    Joined: May 2010
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    wavepropulsion Pirate Member

    As I read in this forum and all around in the web- much people experiment with trimarans and other more or less complicated hulls to have speed and economy- but under my mathematics boats like some Atkins designs for being narrows and light and others like Bolger s Sneakeasy are the more efficient. Also I think the sneakeasy runs better-level at all speeds. I still looking from years ago for a boat of the carachteristics as this bolger design- but better to use in open waters. Under my point of view the sneakeasy can be do a good work with a bit raked sten- a bit of flare in the first third of the boat and probably nothing more. If the boat runs level I think don't need modifications in the bottom- probably a slight vee or a bit rounded in the forefoot. XLNC or R.Russel claim to be seaworthy but I think that boats will run nose up.
    I need suggestions to found a good plan for a boat capable in the chop and in the waves of open waters- capable of good speed with ten hp or so. Also if somebody can suggest me to apply modifications to the Sneakeasy to improve seaworthiness and not loosing of economy - I think this boat can be done in taped seams as well.
    Sorry- my english is not the best but I think is understable- and also I'm not an experienced sailor or builder but I spent a bit of time close to the water.
    I'm a bit familiarizated with the people of this forum- cause for years I was reading your posts to learn several things. So thanks a lot.
     
  2. gonzo
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    gonzo Senior Member

    You need to first define what "good speed" means in knots. Secondly, you need to specify what size boat you are thinking of and what load it is intended to carry.
     
  3. tom28571
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    tom28571 Senior Member

    Bolger's sneakeasy is a long, narrow, flat bottom and lightweight boat that he designed to be very efficient in fuel use with low power in sheltered waters. He said that himself and warned against trying to make it into what it was not meant to be.

    There are still things to be discovered and developed in hull design but the basics have been tried in about all the ways possible. We should all leave room for the newcomer experimenter with fresh ideas but the water and air remain the same forever.
     
  4. wavepropulsion
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    wavepropulsion Pirate Member

    Good speed is something over ten knots and I intend to carry my goods for long weeks and my dog.-with some lucky a gril friend as well if she is pretty enough. The size of the boat as that of the boats I mentioned. Around 20 feet or six meters is good to me with a beam no more than 6. I can catch a nice chop here (in summer three feet waves each five seconds) or bigger waves all the year if I go to the east. I living in the bigger estuary Rio de la Plata- (my location appears being in Spain cause was it when I registered). I got a bit of experience powerboating in Tasmania with small boats as this.
    Bolger suggested- as I read somewhere- to add flaire to that boat. Also Carlston did a bigger version with a seven degrees vee bottom but his boat result in a gas guzzler. I think somer boats are better than sneakeasy but none in the range of the 10to 15 knots.
    I bring my opinion just to ask if somebody know plans already done for boats of the carcahteristics I want. Also I know the basic philosophy of instant boats was to simplify the construction having good qualityes- and in this sense I suppose exist some margin to modify the boat to go stronger and more seaworthy. Cause this I asking. I still looking for the appropiate boat plan since five years ago.
    I owned a 19 feet planning hull I did in taped seams- multichine and narrow with a very fine entry. After using a 4.5 old mercury I found the boat very seaworthy cause the lightness but to go slow at five knots it needs a different bow and a bit of flare ahead. With a better bottom she can sail better as well. So - after time thinking in modify it I prefer to found the plans having already what I want.
     
  5. wavepropulsion
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    wavepropulsion Pirate Member

    Also I'm a bit confused. Some studyes claim the narrow boats of a relation six to one are not only more efficient but also more seaworthy as the Aran currach. Some people looks for beam to have more seaworthiness so........is my confusion. I'm happy if I hear seaworthiness and fuel efficiency go toghether.
     
  6. philSweet
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    philSweet Senior Member

    At the sizes and speeds you are considering, every knot and every foot of length mean a different boat. You are firmly in the semi-planing realm for a two person camp cruiser that's not more than 20'. And a ten knot boat (cruise) would be completely different than a fifteen knot cruiser. Power will go very roughly as the cube of speed and economy with the square of speed. So if a 15 hp could power a ten knot cruiser, expect something like a 50 hp for a comparable fifteen knot cruiser. 15 knots should start to plane out and it might not need quite that much power because the surface area will start to decrease noticeably.

    I suggest you look at the cost of operating the motor for a year and think about how that should relate to the expense of the hull. Hypothetically, if you were planning to spend US 20,000 on the boat over the next five years, How would you divide the cost between the boat itself and the money to run it?

    Once you have a guess at the hull expense, you can estimate the hull weight based on the build method. And from those two items, the rest is pretty tightly constrained.

    It can be difficult to get people interested in optimizing a 10 hp recreational boat because the annual fuel savings probably wouldn't buy a cheap pair of speakers. You might actually get more interest if you asked about optimizing the boat for a cheap audio system.
     
  7. michael pierzga
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    michael pierzga Senior Member

    Long and thin.

    Its the classic formula for a seaworthy, low power boat.

    Used by fisherman all over the world.
     

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  8. philSweet
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    philSweet Senior Member

  9. wavepropulsion
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    wavepropulsion Pirate Member

    Thanks phil for the numbers- I consider it very important. And the highlander looks pretty good and is an option I will consider and I like much Fisher designs (what about the steam launches?). But long and thin is about I was asking because I know exist a ratio considering lenght to beam in additition to Froud's formula for hull speed. And long and thin is was I looking for cause this. Also I know about boats that began to plane before the hull speed -generally light canoes.
    Everybody agree about the boat design still limitated by the market and taxes based in lenght. Normally displacement small boats are fat for being more comfortable -also seworthy at slow speeds I think-. The german S Boats was displacement and faster than the british planning hulls in the rough. An I suppose a small and thin powerboat with certain design to reach semiplaning speed with not much change in trimming can be done with lower expense of petrol or diesel. As the Rescue Minor- under my point of view not much efficient than another one with a more conservative bottom light and thin. But I don't see nothing in the net -no plans- for something like that. If this is impossible tell me I just dreaming.
    I will put a normal car stereo in my boat- with an usb.
     
  10. PAR
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    PAR Yacht Designer/Builder

    I find your conclusions lack an understanding of the fundamentals. As a rule, most that have studied Atkins, wouldn't ever suggest Billy's nor John's designs were light. Not even in their era and certainly not by modern standards. Maybe it would be best to study design and not the hyperbole of those, hoping you'll buy their half century old plans. Don't get me wrong, some of their stuff is wonderful, but light and efficient wouldn't be terms I use to describe it.
     
  11. Mr Efficiency
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    Mr Efficiency Senior Member

    I wouldn't apply the term "seaworthy" to the vessels used by many fishermen, they don't earn enough money in many cases to be able to afford truly seaworthy boats, and I doubt life insurance companies would want their business.
     
  12. michael pierzga
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    michael pierzga Senior Member

    Seaworthy always implied the best bang for the buck. Poor fisherman cant afford a big bang , so they adopt the time tested formula..long, thin, low power.

    I regularly see those long thin fishing boats maintaining good speed 10 to 15 knots upwind against an ocean swell.

    Your bog standard cruiser would by throttle back, stern down, bow up, wallowing at displacement speed while shooting dollar bills out its exhaust pipe.
     
  13. Mr Efficiency
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    Mr Efficiency Senior Member

    Certainly the narrower boat is more sea-kindly under some conditions, but overall is more likely to go belly-up when things really turn bad.
     
  14. Easy Rider
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    Easy Rider Senior Member

    http://www.atkinboatplans.com/Cruisers/Tang.html
    wave,
    If you really like Atkin look at Tang. A bit more power at 35hp but she could be built a lot lighter in plywood. Not much is lighter than plywood. Plenty of deadrise to eat lots of chop and with a good rudder may be excellent in bigger seas. Reducing freeboard a bit and possibly extending her at the stern may help also for your requirements.
    http://www.atkinboatplans.com/Cruisers/Wader.html
    If you like flat bottomed boats "Wader" may work for you too in plywood. Narrow and full displacement if kept light she would do fine with 10hp.

    From what I gather Atkin boats are not "instant boats" but excellent boats.

    Take a look.
     
    Last edited: Aug 5, 2013

  15. wavepropulsion
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    wavepropulsion Pirate Member

    I like both boats- ERider- but better for me is Wader cause power requirements. If I do it in plywood or generally lighter as you suggest no problem with the flotation line?
    Thanks PAR I need to learn- cause this I'm here- you're very wellcomed and ever I follow your posts. The same for all the others.
    I got that plans of the FAO for panga boats- v bottomed- they work with low power and they got great fame of seaworthiness.
     
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