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How much does size matter?

Discussion in 'General Yachting Discussion' started by smaehr, Oct 9, 2010.

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  1. Pascal

    Pascal Senior Member

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    obviously!! at equal speed the longer the LWL the smaller the wake...

    the lowest bridge on the loop is near chicago at 19 to 20'... many boats have hinged radar arches that can be folded down to clear that height.
  2. Capt J

    Capt J Senior Member

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    The Chicago bridges from Lake Michigan to Mississippi river, the lowest clearance is 19'2. The sanitary canal is much less at around 17' I believe.

    The erie canal is limited to 20'2, by a Bridge just north of Troy, NY.

    These measurements are guaranteed at mean high water, but a lot of times there is an extra foot or 2 there due to the water level, but you cannot count on that

    I got a 75' Hatteras MY to Chicago and back and got her height down to 18'6 by lower the radar arch, masthead, etc etc......It took 3 of us a day to get all of the stuff down and 3 hours to get everything back up.
  3. Innomare

    Innomare Senior Member

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    That's a simplification. Are you claiming that a 60-foot sportfisher throws a smaller wake than a 20-foot sailboat when both are motoring at 8 knots?

    It's a matter of hull shape vs. speed, and LWL is only one factor in the hull shape.

    Bruno
  4. NYCAP123

    NYCAP123 Senior Member

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    And a small factor at that. It's water displaced (draft) vs; hull shape (mainly at the stern) and speed that makes the difference. Guys on 50's + tend not to realize (or care) what they are throwing until the radio crackles.
  5. Pascal

    Pascal Senior Member

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    no kidding... I said that in post nr 6!

    you're comparing apples to oranges here, a sailboat hull is full displacement where as a SF is a planning hull. but if you look at two similar hull types the longer hull will go thru the water with less wake at equal speed.
  6. NYCAP123

    NYCAP123 Senior Member

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    You're saying that a 70' SF with an equal beam, draft, transom width, hull design, weight distribution and speed throws a smaller wake than a 50'. You're displacing far more water. Where does it go?
  7. Innomare

    Innomare Senior Member

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    That's exactly my point. The tanker throws a smaller wake not because of its longer WL, but because of its hull shape. I was making the case for the owner to choose whether he really wants an apple or an orange. The size of the orange has a lot less influence and should not be decided by his speed, but by how much interior he wants.

    I understand your point, and I agree that if the shorter boat is sailing exactly at "hump speed" (riding up on his bow wave), the longer boat may still be below its hump speed at that same speed. Yes, in that case the wake of the longer boat may be smaller.** But what if both boats are sailing well below their "hump speed"? Then it's more a function of how much transom area you are dragging through the water, and that will be about the same for both boats (with equal hull design).

    Hence my point: instead of looking for a longer hard-chine planing boat, I would advise the owner to look for a boat with a displacement or semi-displacement hull design. (that is, if river cruising is his thing)

    **I can also think of a scenario when the shorter boat is on plane and the longer boat is still at hump speed. Bigger wake for the longer boat for sure.
  8. Innomare

    Innomare Senior Member

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    That's actually possible at a certain speed (hump speed for the 50' SF). If the stern of the 50' is exactly in the trough (is that correct English?) of the bow wave, it will cause squatting and give a bigger wake. The 70' boat still has 20' behind the trough to keep the boat at even keel and thus it may have a smaller wake.

    Bruno
  9. Pascal

    Pascal Senior Member

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    we can all come with a what if scenario but one case doens't mean much.

    a few years ago a Ft Lauderdale Sherriff yelled at me to slow down in a MINIMUM wake zone (not a no wake zone). I was behind him at a safe distance and his 30' center console was throwing a much larger wake than my 53 at the same speed. must have been around 7kts or so, he was already pushing a bow wave while i was barely leaving a ripple.

    i agree that in theory one would need to buy a diusplacemnt hull if planning to run only in the ICW and rivers, however there may be other considerations... we all know boats are nothing more than a collection of compromises.
  10. Innomare

    Innomare Senior Member

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    Exactly, that's why I thought the following to be too much of a simplification (especially as I was comparing different hull shapes):

    Bruno
  11. DownRun

    DownRun New Member

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    Boat Height on the loop

    To elaborate a little on your boat height for cruising the loop. Coming out of Chicago at mile number 300 of the Illinois Waterway you will need to clear a fixed bridge that is 19'. There is no way around it either

    If you want to cruise the New York State Canal System, Erie Canal, Oswego Canal, and the Champlain Canal, then you will have to clear 15' bridges.

    If you plan on taking the Champlain route Lake Champlain, Chambly Canal, Richelieu River, Saint-Ours Canal, and the St. Lawrence River, a 17' what you will need to clear the bridges.

    Also when it comes to draft 5' is alot better than 6'.
  12. Capt J

    Capt J Senior Member

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    I did the entire great loop with 6' of draft without ever touching bottom. However it limited us as to which marina's we could fit into, and the ones we could fit into were fewer and farther between.

    You can take the New York State canal system, Erie Canal, and go from NYC to Oswego, NY and into Lake Ontario and the lowest bridge you need to clear is 20'2.