Columbian L6 JB three blade bronze cleaver

**paavojaelvis** · 07-17-2017

Phil, you are right with weight distribution. But it's not the way you think. There should be more weight in the rear end. Problem with take off is, this boat lifts its rear end too soon, propeller looses grip and boat comes into halt, well almost...

This hull was designed for dual engine set up (two 500cc Crescent outboards). With Chrysler, i have 65 kilograms less weight at transom. Not to mention my co-driver (7 yrs/28 kg)...

See magazine article about my boat under construction ("Vauhdin Maailma", July 1972). Unfortunately it's in finnish language, but you can enjoy the pics. Attachment 62468

**filthy phill** · 07-17-2017

You need a bow lifting prop. I have problem with bow on mine, once I hit about 36mph the back just keeps lifting.
I Can't put any more weight at back or it would sink at standstill.
But your getting there with that boat, just need to get prop tweaked to give bow lift. Soon be way over 40mph with that.

**Fastjeff57** · 07-21-2017

Maybe I'm all wet on this (hah!) but I've always believed there is no such thing as a 'bow lifting' prop. Props are either stern lifting or neutral,

Ron?

Jeff

**filthy phill** · 07-21-2017

Ahh this is where things get complicated.

A true neutral prop would have zero rake, then it would neither put the bow up ( obviously a slight bit due to forward motion. ) or back up.
Lots of props out there with neutral lift, but mainly on slow or heavy river boats, these give better revers thrust .

I think its one of those chicken v the egg type of things as it depends how you want to look at it.

**zul8tr** · 07-21-2017

Originally Posted by Fastjeff57

Maybe I'm all wet on this (hah!) but I've always believed there is no such thing as a 'bow lifting' prop. Props are either stern lifting or neutral,

Ron?

Jeff

Right on the lifting and neutral but also there is rear dropping case. With rake the direction of changing forces on the blades is very complected depending on submerged or surface piercing prop as they rotate. Rake tilting rearward is + rake and generally more rake drops the stern, the result is the bow goes up, props that lift the stern have low or zero rake. Ex my 3 point hydro props have small 6 degree rake and lift the rear. Lots of rake not needed because there is compressed air under the hull for positive bottom air pressure aero lift up + hydrodynamic water lift up from the the rear plane surface wedge thru the water + aero lift up on the deck to raise the bow. Consideration of the location of the center of gravity needed and all these lifts create induced drag. Hulls with little ability to cram air underneath and not that much deck aero lift (deep Vee jobs etc) need lots of + rake and engine trim out to get the bow up which isn't always the optimum direction for forward thrust force. It is a compromise on these type hulls due to reduced or lack of air lift forces noted for 3 point hydros.

Mccauley on rake:

http://mccauleyandson.com/html/props.html#rake

**paavojaelvis** · 08-13-2017

I modified this prop by adding about 1/2" more rake. Income: comes out of the hole better, even trimmed out (3rd hole). Gained a bit speed, too, now we are above 38 knots (driver only). Still porpoising in calm water, got to check the hull bottom before any more modding.

**paavojaelvis** · 08-13-2017

Had fun with friends in Saturday. Here is some onboard footage, the fun part starts at 5.40... https://www.youtube.com/watch?v=JDFPGljIgY8&t=14s

**Fastjeff57** · 08-13-2017

How did you add more rake? Weld on the blades?

Curious.

Jeff (home made props maker)

**filthy phill** · 08-13-2017

Looks like the motor is running very good for you.
that porpoising will never go unless you trim it out a touch more, motor is not running level enough causing the front to keep dropping.
you will get another 2 to 3 mph atleast by trimming it out a bit more.

you had a good bit of fun with it though, I need to get mine out this week if weather holds up.

and what happened at the end of video ? run out of gas

you cannot add more rake to the prop without taking the blades off cutting to different shape then welding back on (very dangerous), you can put cup in the tips to
act like a touch of extra rake, but rake is the blade angle to the hub.
Maybe you mean added pitch.