Correct Engine Height / Trim

[Johnnielund]

I have a 2007 Lund 1700 Explorer Tiller model. (1035 dry weight) powered by a 2008 75 HP E-Tec. The E-Tec is rigged on the second hole from the top (recomended by most dealers). This puts the AV plate even with the bottom of the "V" in the hull. I also have a bow mounted MinnKota Terrova trolling motor. I'm turning 5300 RPM (should be turning 5200 minimum) with a PowerTech 13.25 x 16 OST (supposed to be comparable to BRP "SST") stainless prop, and get 39.5 MPH GPS ground speed at WOT. Now the part I don't understand. When I am trimmed out high enough to achieve WOT 5300 RPM the boat will start to chine walk (this does not happen to deep "V" boats at 40 MPH, only to Bass Boats at 65+ MPH). If I trim back in to regain better steering control, the RPM drops off. Do I raise the engine 1 hole and not trim out as much? Lower it one hole, alowing more trim angle resulting in a more bow up attitude? Change to a lower pitch prop? Change to a prop that would give more bow lift. I have 30 days to be able to exchange my prop.
It almost seems to me that the bow rides too low and when I hit a slight wave / wake thats when the stern starts to break loose. Thank you all for your input.

 

[Dhadley]

Re: Correct Engine Height / Trim

Is it chine walking or porposing?

 

[Johnnielund]

Re: Correct Engine Height / Trim

To be very specific, this is what happened. Lake conditions were a slight ripple on the water. I was testing my new prop (13.25 x 16). I had a BRP SST 13.38 x 17 and could not get the RPM up high enough. There were two of us in the boat. I was in the stern and there was one more person sitting on the seat just aft of the casting platform. I opened the throttle to wide open and jumped right up on plane. Then I started to trim up to the highest RPM, then back down a little. The RPM was 5300 and I had 39.5 MPH gps ground speed. A PWC crossed in front of me resulting in a small wake. When my bow, or keel hit the wake the stern broke loose and I started to rock side to side (chine walk?). It was almost like I had lost directional control. I trimmed down and came off the throtle and got steering control back. This was kind of a spooky feeling.
Any suggestions?

 

[Dhadley]

Re: Correct Engine Height / Trim

Personally I'd put the SST back on and raise the motor a little. That should gain some rpm and maintain control.

 

[Johnnielund]

Re: Correct Engine Height / Trim

OK. I'll have to send the SST in for repair, as it met up with a big rock on the Wisconsin river and the rock won. Fortunately I was going slow so the only other damage sustained was a slight gouge / nick in the skeg. Biggest reason I went with PowerTech is they have an exchange program. All my local dealers look at props as "you bought it you own it, if you want to try something else, buy it"

 

[Dhadley]

Re: Correct Engine Height / Trim

That has a lot to do with the fact few dealers understand props. When looking for another prop you'll need to compare what you've tested to what you need. Compare the style of everything you've tried / tetsed vs. a (possibly) different style. Look at the set up / use / dsriving style. How's the balance? Are you looking for more bow lift at less positive trim? Do you have to overtrim with what you've tested? What's the percentage of slip of what you have? % of slip on the new prop you tried?