prop height

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wildman.XD

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Jan 11, 2010
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7
i bought a 1975-1980 20hp mercury tiller with plans of putting it on a 14' jonboat but instead i found a good deal on this boat its 16' by 56" but the prop only goes down to the bottom of the boat were i put the red circle does it need to be under the boat and how far? iboat.jpg
 
Bondo

Bondo

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70,524
Re: prop height

Ayuh,... The flat plate, just above the prop, should be Even with the keel line....
 
S

steelespike

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Apr 26, 2002
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19,069
Re: prop height

It appears to me you need a long shaft motor.Or if the transom needs work you could cut it down.I wouldn't mess with the transom otherwise.
A 20 may be challenged on a boat that heavy.I wouldn't hesitate if it was a bare bones aluminum.My bare bones 18' Crestliner did exceptionally well with an old Gale 25.If the jon was shorter and narrower at the bottom the 16 my be ok but for the weight.
 
E

ENSIGN

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Re: prop height

Did you have to pay for the boat to.:redface:
 
M

mpsyamaha

Petty Officer 1st Class
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Jun 8, 2007
Messages
395
Re: prop height

thats a 20" transom, and that hull is rated for up to 75hp. i used to have that boat, but a lot newer and nicer. it was nice with a 70hp 2 stroke yamaha.

newrsxwheels019.jpg

newrsxwheels015.jpg
 
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wildman.XD

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Jan 11, 2010
Messages
7
Re: prop height

yeh i got that p.o.s. for $400 with the trailor..im 21 and this is my first boat..i just wanted somethin that floats and can take out the ladys ;)..oh yeah and how slow is this thing really gunna be?
 
E

ENSIGN

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Re: prop height

Well don't tell the girls that were going water skiing,Maybe a moonlight cruse will be a better idea:rolleyes:
 
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wildman.XD

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Re: prop height

Well if i cut the transom down to were the anti ventilation plate is supost to sit right that gives me about 6" or 7" to the waterline and i dont really know much but that just sounds unsafe.lol. is that just the way to go or is there a bracket or somethin that would be better for this problem? :confused:
 
smokeonthewater

smokeonthewater

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Dec 3, 2009
Messages
9,838
Re: prop height

don't cut the transom.... sell your engine and buy a bigger engine..... at least 40 hp that fits the boat
 
S

steelespike

Supreme Mariner
Joined
Apr 26, 2002
Messages
19,069
Re: prop height

Don't cut the transom try to trade up to a long shaft motor with more hp.
That boat with a 20 might do about 23-25 mph when very light.Start loading in people and you will be lucky to plane with 3 aboard.We used to ski with the 25 on the 18' Crestliner but we had a 100lb adult spotter.
Measure from the bracket where it rests on the transom to the antivent(cavitation) plate just above the prop.If you cut the transom you may be able to cheat a little.
Before you cut anything throw the motor on the boast and put it in the water
Measure to the water with you in the boat.I would think that a regular hull 15" transom would have about 10" to the water.
 
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wildman.XD

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Messages
7
Re: prop height

how about this bracket its 1 1/2'' thick poly mount board, 8'' width, for motors up to 15hp fixedmountmotorbracket.jpg
 
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steelespike

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Messages
19,069
Re: prop height

First thing is its not rated for 20 hp.A 20 is over 30% higher than the rating.As you lower the motor will it have room to turn,clearance to be tilted up?
Also something I hadn't thought of; due to the deep V to get the motor low enough it may be threatened with flooding (water) under certain conditions.
 
J

Jeep Man

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Oct 17, 2008
Messages
2,803
Re: prop height

Cutting the transom or adding a bracket to lower the motor would put the cowl portion too close to the water's surface, risking swamping it. Sell your motor for whatever you can get and pick up a good long shaft of appropriate horsepower.
 
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wildman.XD

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Jan 11, 2010
Messages
7
Re: prop height

i put the motor on craigslist for $600..how much would a decent 50-75hp cost it doesnt have to be the prettiest as long as it runs strong and will last a couple more years and what do you guys think is a 75hp too big? and if anyone has a motor that would fit nice email me sureal350@gmail.com
 
smokeonthewater

smokeonthewater

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Re: prop height

I just threw those up for a price reference..... that merc sure looked pretty tho lol
 
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wildman.XD

Cadet
Joined
Jan 11, 2010
Messages
7
Re: prop height

yeah it does ive got the same one in black but its a 20hp if you go to miami craigslist under 20hp mercury youll see it. i put it up for $600 and a couple of ppl already called me
 
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