Re: Venting the prop ?
I did as much research as I could before attempting this. Unfortunately, i didn't find much out there. I have a 90hp 4 stroke on a 17' aluminum DC. I typically run a 19" prop which has a WOT @ about 5400; WOT range for this motor is 5000-6000. I also typically have rather heavy loads as I keep a fair amount of equipment on board. When it's just my wife and I, acceleration is adequate with this prop but I choose it because it is nice for cruising. Whenever I go out with a couple of buddies (extra few hundred pounds anyway), there is a lot of weight in the back of the boat, especially considering I have a 4 stroke and also with a full tank of gas. Planing can be a bit of a task here with the 19" prop. Without the 'Dol-Fin', I might night even be able to plane without filling front live well or standing up. But overall, my concern is with the load it places on the motor. Therefore, I often switch to the 17" prop I have. Typically, this means changing a prop every weekend or sometimes within the weekend.<br />For this reason, I wanted to experiment with venting the props. After researching abit, I drilled three 6mm (7/32") holes, at a small angle on the trailing edge of each prop; just like the illustrations on the links associated with this topic in this forum. Yesterday, I tried the prop on calm water with two couples on board and a full tank of gas. I immediately noticed a quick throttle response from idle when advancing the throttle slowly. However, there was very little acceleration. It almost seemed like I could run the motor at 1000 rpm or 2000 rpm and go the same speed. Advancing the throttle more into the hump yeilded a mushy feel. the motor definately sounded like it was spinning faster without a corresponding linear increase in speed. It alsmost felt like a spun hub. Actually, the best way i can think to describe it was like I had only 1 or 2 blades that were doing the work and the other one(s) weren't; it was a very unbalanced feel to it. The biggest surprise to me though was that even while planing at around 20 mph, a sudden increase in throttle seemed to also be lacking in an accompanying increase in acceleration; almost like the prop was still ventilating abit. The boat also seemed very bouncy, not porpoising but like I was in 1 foot waves even though there was absolutely no winds. I know a prop can make a difference in bow lift etc and was wondering if these holes were somehow change how the boat ran while underway. It was an open lake and there alot of very small rollers of inconsistent periods. But the boat just seemed very bumpy for the conditions.<br />I any case, i was quite unimpressed with the results so much so that I did not continue the trip without changing down to the 17" prop without the ventilation holes. Anyone have advice on what I observed? should I make the holes bigger ( No where have i seen drilling holes smaller than 6mm (7/32") as a astarting point). Is there a way to refill the holes without taking it to a shop?<br />Curious to know what others who have tried this have observed.
