2005 Merc 40m mods for river racing

[Cubman]

How was the yamaha prop modified to allow you to go from 3" above to 6" above?

[Cajun]

How was the yamaha prop modified to allow you to go from 3" above to 6" above?

I do not bend propellers correctly or on purpose. My prop was modified by someone that modifies propellers for a living. Just like I did when I raced and he did my props, I told him what I wanted to accomplish and let him use his knowledge to attain that. I have zero cavitation, no motor shaking, no torque? I wanted as close to an all purpose propeller as we could get. I run this prop when empty, and I run this prop with 3 other guys and gear in the boat. Only time I don't run this prop is to tow another boat, I use a smaller pitch spare I keep in the boat.
So to answer your question, I do not know everything he did to the propeller.
D

[88workcar]

6" above the transom as will my Quicksilver Trophy Sports, my 12" diameter quicksilver cleaver will run 8" above the transom.
Di

How does this translate to propshaft hight in relation to the bottom of the hull?

[microbream]

Here's the pics of the bottom of the boat that I promised. Sorry for the late response. I tried to take the best pics I could with the boat on the trailer. Let me know what ya'll think about where to put the angle aluminum and how wide the pad should be. I have a bunch of .080 aluminum around the house and I could get some 1" or 2" angle to make the "air entrapment" that ya'll speak of. Thanks.

Cory

I recently made a pad to suit my shallow vee bottom. The dimensions were very much guess work and scaled from bigger boats. However it is 240mm wide at the stern and tapers down to 60mm at the bow. All edges are sharp, straight and it is perfectly flat.
Trust me i picked up 600rpm at the top end straight away, probably need another repitch to make the most of it. I can now hit 33mph with just 8hp on the back!
as far as porpoising goes, i just drive right though it!!!
cheers
kael

[Cajun]

How does this translate to propshaft hight in relation to the bottom of the hull?

Don't know, I'll shoot a pic later today. The transom is 21" tall, the motor is mounted 3" above the transom at it's lowest point, and the lift plate will rise 6" while underway. So I was mistaken, the 12" diameter will run 9" above the transom for a total of 30" height from the bottom of the boat to the clamp bracket on the motor. I am water pressure limited. It drops from 27# of pressure to about 5# at that height. I do not care to modify the gearcase and water intake. Like I said, I'm gettin to old for those impromptu swimming trips.
D

[Cajun]

How does this translate to propshaft hight in relation to the bottom of the hull?

I originally thought I could run much higher when I first saw the bottom design on this hull. After testing the hull, it rides so high when up on plane, that limits the height the motor can run. Watch the video, it runs very high, more like a padded hi perf bass boat than an aluminum hull.
http://s126.photobucket.com/albums/p...rent=good3.mp4

He ya go. Please note, that is a fishing prop on the motor, not my 12" diameter cleaver. With the plate raised to it's full height, the cav plate is 4.75" above the bottom of the V on the boat. The prop you see on the boat runs about 2-3" lower than the cleaver.

[Ballistic]

Note that the more setback you have, the higher you can raise your engine.

[Cajun]

Note that the more setback you have, the higher you can raise your engine.

You are exactly correct. The point of diminishing return for us was over 10". We gained height fairly proportionate as we went up to 10". When we went past 10", we could not raise much more until we went to right at 18" setback, then we began to gain more height. 18" is not really acceptable with a tiller, around 12" it starts to get difficult to reach the tiller. We were testing a 3 cylinder Merc.
D

[Cubman]

Cajun,

I have read a post of yours on another forum that said a 16' boat will run 3-4mph slower than a 15' boat. What can I do to minimize this? I assume it is mostly the weight distribution?

[Cajun]

Cajun,

I have read a post of yours on another forum that said a 16' boat will run 3-4mph slower than a 15' boat. What can I do to minimize this? I assume it is mostly the weight distribution?

Don't know. we have tried everything and canot make them run the same. Don't know if it's the weight or the fulcrum point is further forward tha n the fulcrum point on a 15' boat.
D