Bigger Motor?

Discussion in 'Outboards' started by valvebounce, Oct 4, 2016.

  1. valvebounce
    Joined: Dec 2010
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    valvebounce Senior Member

    Thanks Ike,
    I'm glad you worked the square root out,it's a long time since I used it.
    Well,that's Gerald and yourself in agreement that the18hp should do the deed.
    I'm glad to hear it,I spent a lot of time bringing the engine back,and it runs sweet.
    The fact that I have done the mechanics on it and can trust it goes a long way.
    The guy I bought it off didn't mention what type of boat it had been on,it may have even been a 30ft steel barge.(max 6mph speed limit) on UK rivers and canals.
    Things are looking like you are both right about the prop pitch.
    I can't get over he fact that I am in touch with someone in Alaska and Washington DC.
    This site is spot on.
     
  2. Commuter Boats
    Joined: Oct 2006
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    Location: Southeast Alaska

    Commuter Boats Commuter Boats

    Good morning valvebounce, I'm glad we've been able to renew some confidence in your project and looking forward to seeing the photos. Ike is almost a neighbor of mine at a mere 700 miles south in a little east of me in the state of Washington, we are both half the world around from you :)
    Gerald
     
  3. Ike
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    Ike Senior Member

    I cheated. I used a scientific calculator. I haven't actually worked out a square root since Hewlett Packard invented the hand held calculator. And before that I used a slide rule.
     
  4. valvebounce
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    valvebounce Senior Member

    Hello again Gerald,
    I googled South east Alaska,the place looks fantastic.
    My brother has the pics in hand.
     
  5. valvebounce
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    valvebounce Senior Member

    Haha,my dad was the last person I saw using a sliderule,he was a design draftsman for A.V,
    Roes.He was offered a job at Acme rockets way back in the 60's.
     
  6. Ike
    Joined: Apr 2006
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    Ike Senior Member

    In the early 70's I worked in the Naval Architecture department of a major shipyard. We used slide rules a lot (I still have the first one I bought and a collection of various slide rules as well. Someday I'll donate them to a museum). But in 1971 (or 72) we (the shipyard) bought an electronic calculator, as big as a typewriter. About the same time HP came out with the first hand held, and after that we never looked back.
     
  7. valvebounce
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    valvebounce Senior Member

    We have still got some of my dad's bits and bobs,french curves etc.
    He was a chief petty officer in the royal navy during ww2.Still got his medals.
    He took a lot with him knowledge wise when he went.
     
  8. Ike
    Joined: Apr 2006
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    Ike Senior Member

    A CPO. He has my highest regards. I never got that far as an enlisted man, I jumped over it and went direct to Ensign.
     
  9. valvebounce
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    valvebounce Senior Member

    The US and Royal navies certainly put a life stamp on a way of life,luckily,I got some of it passed on.
     
  10. valvebounce
    Joined: Dec 2010
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    valvebounce Senior Member

    Hi Gerald and Ike,
    My brother has taken the pics.
    I took the prop off and the number is--9.25"dia and 11" pitch
    I researched the prop at formula prop .
    For a 12' to 14' boat they recommend 2 props,the one that I have and a 9"dia x10" pitch.

    For a 14' to 16' boat they recommend a 9" dia x 9" pitch.

    In theory the 1" reduction in pitch would increase the the max revs by 150 to 200 rpm.
    So I am wondering if that would do,or leave the planing capabilities borderline.

    For the 14' to 16' boat they recommend a 9" x 9",which would bring the max revs capabilty
    up by 300rpm to 400rpm.
    To avoid being dissapointed,I am thinking the 9x9 would be the best bet.
    There is no rev counter on the boat,but I could judge the max revs to stop it over revving.
    Any opinions on my choice?
     
  11. Ike
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    Ike Senior Member

    I am no expert on props but I think the 9 X 9 will serve your purpose. However, try it out and if it doesn't work out return it and get the 9 X 10.
     
  12. ondarvr
    Joined: Dec 2005
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    ondarvr Senior Member

    There is no way to dial in prop without a tach, you can't estimate RPMs. You can get a cheap tach on ebay for about $10.00.
     
  13. valvebounce
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    valvebounce Senior Member

    Hi Ike,
    that's the conclusion I reached,I'm glad you agree.
    You wouldn't believe the difference in price between the UK and USA.
    Anything marine/sport over here and they whack the price up.
    I needed a fuel pump for a 6hp Evinrude,it worked out £7 cheaper to get it from New York,pay the postage and customs charges etc.
    £7 wouldn't break the bank obviously,but I got it from New York on principal.
    Let's hope the new trade deals come to the fore when you get a new president.
    Have a nice day
     
  14. valvebounce
    Joined: Dec 2010
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    valvebounce Senior Member

    It's certainly worth considering,

    I wouldn't have a clue where to fit a tacho though,especially on this old engine.
    It's a pull start with no electrics.
    I have to set the throttle near the steering,go to the back and fire it up.
    Outboards have been a learning curve for me,getting more revs out of an engine on a car
    or bike has been the aim over the years,but outboards are a different ball game.
    Interesting though.
     

  15. Commuter Boats
    Joined: Oct 2006
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    Commuter Boats Commuter Boats

    I'm going to agree with ondarvr that you really need a tach but I don't think you need to buy one, I think you should be over borrower one that you simply point at the flywheel or push a little rubber tip against the nut in the center of the flywheel and it will read out RPM.
    As to the propeller, I'd start with the 9x10, I'm under the opinion that the problem with the previous prop wasn't that it was too much pitch but that its geometry was screwed up... I have nothing tangible to prove that, it's just my gut feeling.
    Gerald
     
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