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HP vs Pitch vs Blades ????
WhalerSailor	#1  Posted on 05/21/07 - 11:36 AM
Member Posts: 9 Comments: 1 Joined: 08/05/06	Cheers all, I have a friend who has just retro fitted his 13' Whaler with a 1962 Merc 500. This is one clean Merc 500. Great compression! Looks and runs like new. We fitted it to the boat and took it out last week with the old two blade prop which came on it. The engine ran great all day but would only reach a top speed of 23 MPH and the motor was sounding like it was revved too high. As of now we haven't installed a tach (coming soon). Yesterday he put a three blade Michigan wheel prop on it and could not achieve WOT (nowhere near it) and a top speed of 12 MPH. Both props are 13 pitch. Is there such a thing as setting the dwell or point setting to match a prop (ie. two vs three blade)? I used to have an old VW with no power - cleaned and set the points and she took off! I know these props were sold as standard props for as little as 35 HP and his boat is small and light. Any insight would help immensely. Thanks, Dave
moose	#2  Posted on 05/21/07 - 12:45 PM
Member Personal Page Posts: 543 Comments: 1 Joined: 03/07/07	Dave, Something seems very wrong. Is it an older 13 with a short transom? How were you determining your speed? How about trim? I have a Nissan 40 hp tldi on my 1068 13'. It came with a 12" pitch prop and I couldnot run wot. It reached the max rpm way before wot. I put a 15" prop on it and it flies. With one person in it I can accelerate through the porpoising and then begin trimming the motor out. I got the rpms up to 5700 and 45.1 mph on the gps. It's really exciting but NOT SAFE! I'm changing to less pitch soon. Mike
WhalerSailor	#3  Posted on 05/22/07 - 1:42 AM
Member Posts: 9 Comments: 1 Joined: 08/05/06	Thanks for the reply Moose, Speed is measured by GPS. It's a long shaft with the cavitation plate running just about 1/2 inch below the bottom of the keel (that's as high as I could get it). Your answer is part of what I'm confused about. If you are reaching max rpm before wot, why would you go to a smaller pitch? Wouldn't that be racing your engine even higher? Dave
moose	#4  Posted on 05/22/07 - 7:03 AM
Member Personal Page Posts: 543 Comments: 1 Joined: 03/07/07	Dave, I see that I was unclear in my post. With the 12" pitch prop the motor would reach max rpm before the throttle was pushed all the way to wot. There is a rev limiter on the motor and it would keep it from going over 5800 rpm and the alarm would sound. Also, it's a 1968, not a 1068. Mike
Nobleskydiver	#5  Posted on 03/14/08 - 8:28 PM
Member Posts: 18 Comments: 0 Joined: 11/11/07	Evening, On my 20 hp 2 stoke I had a two blade and it was fast as I was solo pilot, when I loaded teh 13' with diving gear and open ocean I went to three blade Merc only showed two types props for that small engine, I just found this web site http://www.piranha.com and learned a little. RPM and speed is important as well as type boat, I guessing our whalers are planing hulls at least the older classics as compared to newer model. Not sure what else to say but I seen many a 50 hp on these 13 footers not to many worries,. JMO from the saddle Bill
Phil T	#6  Posted on 03/15/08 - 10:32 AM
Administrator Personal Page Personal Album Project Albums Posts: 6994 Comments: 6 Joined: 03/26/05	Dave - While the others can help you work out the prop, I have a separate suggestion. Given the current mounting, have you considered a jack plate so you can raise up the engine. Getting the anti-cavitation plate above the keel by 1/2 to 1" will add to the performance. Many owners with a long shaft add a jack plate. The only consideration is the added weight (20 + lbs) in the stern. 1992 Outrage 17 I 2019 E-TEC 90, Viper 17 2+ 2018 Load Rite Elite 18280096VT
kamie	#7  Posted on 03/16/08 - 6:02 AM
Member Personal Page Project Albums Posts: 2975 Comments: 3 Joined: 11/04/05	CBO is correct, until you jack that engine out of the water you can play with props all day and not go very far or very fast. Check out T&H or Cook CMC Cook for jackplates and products designed to retro fit a long shaft motor on a boat designed for a short shaft.
Binkie	#8  Posted on 03/17/08 - 7:46 AM
Member Personal Page Posts: 2012 Comments: 0 Joined: 12/19/05	I would try a 17pitch prop, When you say that the motor is as high as it can go, do you mean you have put shim sticks between the clamp bracket and the transom. If not add a 1/2 shim stick to at least get the cavitation plate level with the bottom. It would be optimal to be 1/2" to 1' above bottom. If you don`t have tim-n-tilt, adjust the tilt pin so the motor is vertical or slightly kicked out. Also decarb the motor, and you will see a difference. Rich
Binkie	#9  Posted on 03/17/08 - 7:47 AM
Member Personal Page Posts: 2012 Comments: 0 Joined: 12/19/05	duplicate Edited by Tom W Clark on 03/21/08 - 10:11 AM