Model Boat Mayhem
Mess Deck: General Section => Full Scale Ships => Topic started by: hemayann on April 17, 2012, 10:25:02 am
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i have a motor thats marine 39hp, the shaft is 1200mm, what size boat and prop can it handle?
i need a formula?
does it matter how long the shaft is?
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39 horse power should get you across the pond. %)
ken
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ha its for a big boat :-))
na i've got a 25 ft clinker boat its got a 12hp yanmar n a 28mm saft n a big prop
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is that a full scale boat??
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1 to 1 scale
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out my depth here {:-{
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(http://s11.postimage.org/qq2p5l9wf/DSCN0678.jpg) (http://postimage.org/image/qq2p5l9wf/)
(http://s11.postimage.org/677t0ivz3/DSCN0676.jpg) (http://postimage.org/image/677t0ivz3/)
here she is
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Think you need to join this lot matey .....They might have a lot more knowledge about this sort of thing than we mere modelling mortals will have about the subject........
http://www.classicboat.co.uk/forums/forumdisplay.php?f=17
neil.
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I suppose the principle is the same but on a larger scale. When we over prop we get heat and smoke but were on the bankside not sat in the boat smoking with it! %% %%
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Be nice to see it with a brushless setup {-)
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ha i know there is some brainy people on here
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Size of boat and prop will depend on whether you want to go watersking really {-)
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ha i know there is some brainy people on here
well, a good question like yours brings out the brainiest of us, lol {-) {-) {-)
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yes there are several formulas kicking around, along with several charts to give an approximation of:
: prop size and pitch for a known horsepower and rpm of the motor
: if the boat's weight and size are known & you know what speed you wish to go - there is a formula for that as well
but first of all; you need several known factors
output shaft rpm of the motor, weight of the boat (in this case its going to be a displacement weight) and we need to calculate the block co-efficient
For a semi displacement hull, the block co-efficient should fall between 0.4 - 0.45
For a displacement hull, the block co-efficient should be between 0.45 - 0.55
K = speed in knots
Bhp = brake horse power at the propeller
K x √bhp
displacement in tons
This should give you some idea of the formula which you require
Aye
john
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^^^^^
told you there is some brainy people here
cheers mate it'll help lots