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Old 01-09-2019, 11:20 AM   #41
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Sounds like 37hp is working good for you. I don't know what your boat weighs and of course it's quite a bit larger than mine. Mine I believe will weigh about 7000lbs. when finished and I'm using a two cylinder Lister Petter LPWS which rather than using the 20hp @ 3000rpm rating I'm putting a fuel stop at 2600 which will be 18hp intermittent and 16.7 continuous. I have a 3 to 1 PRM150 hydraulic gear to a 1.25" shaft and a 18x14 three blade propeller. The boat originally had a Perkins 4-108 with a BW 72c 2.57 to 1 which was turning a 17x16 four blade prop. With the Perkins the boat had way more power than it needed but of course it was a military boat designed to carry 20 men and two crew.
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Old 01-09-2019, 12:32 PM   #42
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+1 on Boatdiesel prop calculator. The site also has invaluable information on most marine gears, engines and gensets.
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Old 01-09-2019, 12:53 PM   #43
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I've used it for several years and have found the calculators to be pretty accurate.
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Old 01-14-2019, 02:39 PM   #44
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Prop

Years ago I built a workboat. My friend worked for Ford Lehman and we put a Ford Lehman 120 with a Warner 73 3-1. I put a 26 x 14 inch. Later the boat was repowered with a John Deere 6 cyl.
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Old 01-14-2019, 02:45 PM   #45
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Mtoa

Join the Marine Trader Owners Association, you can get the right answer there
https://mtoa.clubexpress.com/content.aspx?sl=1076077805

Having. Hundreds of owners respond who own the exact same vessel is priceless.
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Old 01-14-2019, 02:46 PM   #46
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That is a great calculator.
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Old 01-14-2019, 02:51 PM   #47
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My 26 foot workboat with a Warner 73, 3-1 Red, 26-14 inch 4 blade.
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Old 01-14-2019, 02:53 PM   #48
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Quote:
Originally Posted by psneeld View Post
I just for the first time used the basic BoatDiesel prop calculator.

With just the basics, that included prop diameter, it recommended the same size as what was on the boat when I bought it. It is 4 bladed but I think they were originally sold with 3 blades.

I did the same and it came out on what I currently have.
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Old 01-14-2019, 03:36 PM   #49
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Prop

Might want to send the present propeller to a prop shop for repair and rebalancing. May be cheaper and provide excellent results.
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Old 01-14-2019, 03:39 PM   #50
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Every prop manufacturer has a form you can fill out online at no charge which, if you have all the pertinent information, should give you their recommended prop for your boat.
Do several and see what the professionals have to say.
Your boat or someone with the identical boat could have lots of changes over the 40-year lifespan of this boat. One may have a different trany, gear ratio or shaft size, which will lead you astray.
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Old 01-14-2019, 05:11 PM   #51
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Several prop shops I've talked to just use the Boatdiesel calculator. I've checked a number of props on Boatdiesel and then did the calculation using Dave Gerr's Propeller book and they all matched. The advantage of having a prop shop spec your propeller would that if it's wrong they I assume would make it right, never having had that scenario I'm not sure though.
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Old 01-14-2019, 05:15 PM   #52
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Originally Posted by Tugalert View Post
My 26 foot workboat with a Warner 73, 3-1 Red, 26-14 inch 4 blade.
Is that a Walters keel cooler hiding behind that rebar?
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Old 01-14-2019, 05:33 PM   #53
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Yes, The boat was built for me in 1982 by Yank Boat Works of Tuckerhoe.NJ. My friend Walter who worked at Lehman was able to get me the engine, keel cooler, prop, 2 inch shaft, at Lehman cost. Yanks Boat Eorks did
the steel work. The original mast came off a USCG 30 footer that I ran boat while in the CG. As built in 1982 the paint came from TEXACO Marine where I worked as mate on the tug TEXACO Sky Chief. Named after my son the boat is surely a "One Piece At A Time" boat. Lol
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Old 01-14-2019, 05:56 PM   #54
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Originally Posted by Fish53 View Post
Several prop shops I've talked to just use the Boatdiesel calculator. I've checked a number of props on Boatdiesel and then did the calculation using Dave Gerr's Propeller book and they all matched. The advantage of having a prop shop spec your propeller would that if it's wrong they I assume would make it right, never having had that scenario I'm not sure though.
I can't count the number of times I've had to have a prop shop tweak (change the pitch) a new prop to get absolutely the best performance out of it. The actual tweaking is usually included in the deal, if necessary, but if you are not a diver that end can get a bit expensive.
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Old 01-14-2019, 07:06 PM   #55
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I can't count the number of times I've had to have a prop shop tweak (change the pitch) a new prop to get absolutely the best performance out of it. The actual tweaking is usually included in the deal, if necessary, but if you are not a diver that end can get a bit expensive.
I just let the tide go out if I need to remove/replace my props. The only time I've ever had to have the pitch changed on a prop was when I bought a used prop from another boat an inch or so off on pitch.
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Old 01-14-2019, 07:14 PM   #56
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Originally Posted by Tugalert View Post
Yes, The boat was built for me in 1982 by Yank Boat Works of Tuckerhoe.NJ. My friend Walter who worked at Lehman was able to get me the engine, keel cooler, prop, 2 inch shaft, at Lehman cost. Yanks Boat Eorks did
the steel work. The original mast came off a USCG 30 footer that I ran boat while in the CG. As built in 1982 the paint came from TEXACO Marine where I worked as mate on the tug TEXACO Sky Chief. Named after my son the boat is surely a "One Piece At A Time" boat. Lol
I almost bought a little tug similar to yours, it had a Detroit 110 and was 31'. I was thinking of doing commercial towing on the Erie canal. I used to live near the canal in Spencerport, sort of a nostalgia thing. Nice boat.
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Old 01-14-2019, 11:42 PM   #57
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Jeff -- there are a lot of good information being supplied by members is great but I will guarantee you will never reach your desired goal if the tachometer is not calibrated properly -- for about $35 you can buy an optical tach and make sure the tach you are propping to is reading correctly. Saves a boat load of money in wrong props.
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Old 01-15-2019, 04:00 AM   #58
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Jeff -- there are a lot of good information being supplied by members is great but I will guarantee you will never reach your desired goal if the tachometer is not calibrated properly -- for about $35 you can buy an optical tach and make sure the tach you are propping to is reading correctly. Saves a boat load of money in wrong props.
Great point, I think I paid a bit more than that for mine ($200?) but it's a handy tool. Another thing that's quite helpful is a pyrometer which can be had for around $100.00 and gives a much better indication of engine load.
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Old 01-15-2019, 09:49 AM   #59
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Just to add what might be useless information, I like to evaluate what's known as "propulsion efficiency." That's nothing more than the speed of the boat divided by the speed it would go if the prop was not slipping in the water. The efficiency of my sailboat prop was about 55%, my tug is 65% and airplane propellers are about 85%. So, at 10 knots, 2500 rpm, 2.5 gearbox, 65% propulsion efficiency gives a prop pitch of 18.6 inches. Interesting how close it is to the other answers. The equation is: Pitch(in) = boat speed(kts) X gear ratio X 1207(constant) / engine speed(rpm) / propulsion efficiency.
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Old 01-15-2019, 10:16 AM   #60
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The hardest item to enter in most calculations is the actual weight of the boat.

Perhaps selecting a yard that can weigh the boat for the next bottom job might pay ?
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