TOPIC: Tuning up the Hydrodyne Thoughts

A week ago I installed new SX Trim tabs and now the bow rise has been eliminated! I noticed the top end speed is a little slower, but it immediately planes out! I'm running open throttle around 4000rpm. I used to run without the tabs around 4500rpm open throttle. Today, I installed a new aluminum propeller, same diameter and pitch as the old bronze one. This new prop is about half the weight! Should the boat run faster now with less weight on the outdrive? Should I try to adjust the throttle to get some more gas out of it and higher rpms? I'm assuming it will run higher rpms just with the lighter prop? My engine is the Volvo Penta BB70 80hp. Thanks for the thoughts FG Family!

I'm no expert but you may get a little more out if it from the lighter prop but not much. The trim tabs are naturally going to be more drag on the boat, more drag less speed etc..

Bob

I would definitely check your throttle to make sure you're getting all you are supposed to, I believe you tuned the motor recently as well? What pitch prop are you running? I'm no expert on prop selection for inboards, but you may need to drop down a notch? 4000 at WOT seems a little low to me.

I heard something one time I do not know if it is true but here we go. I heard that aluminum props would flex slightly under load and stainless steel props would not. If that is correct I would guess your bronze one would be stiffer as well.

Well, I'm kind of limited on props. Hard to find a 12 splined 3 blade for a volvo...but I did find an identical one to my bronze prop. The new aluminum is 12 1/2 x 15. The parts book calls for 12 x 15, but this one looks identical to my original bronze prop. I also have a new smaller aluminum prop which looks to be about same diameter and a little less in pitch. With only 80hp, I really wonder if aluminum would flex at all? The parts book also suggests a 2 blade at 13 1/4 x 15.