JoLin
Vice Admiral
- Joined
- Aug 18, 2007
- Messages
- 5,146
It's the boat in my sig and avatar. Planing hull, approx. 9500 lbs as tested today. 4 barrel 4.3's putting out 225 hp per engine. Both engines are in excellent state of tune. Recommended WOT range is 4400-4800 RPM. Current props are Merc 'Vengeance' 3-blade stainless with 19P.
Calm water and light breeze for a change, so I took her out for a top speed run. Wide open, both engines maxed out at 4800 rpm (top of the range) and I hit a top speed of 33+ knots/ 38-39 mph on GPS. That surprised me. I didn't expect her to be that fast. I seldom cruise at anything faster than 3600 rpm/26-27 mph. The water is normally too rough for comfort at higher speeds, so keep in mind that top speed is not my concern.
The issue - I can normally stay on plane down to about 20 mph/3100-3200 rpm. It's iffy below that, and I'll usually slowly 'fall off' If I drop the rpm's any lower. That's problematic when I convoy with friends that have larger inboard boats and cruise at around 18 mph. I'd like to be able to stay on plane at a couple mph slower than I can now. In those conditions, engine efficiency and mpg aren't my primary concerns- it's about staying with the group.
On a previous boat (same goal- lower planing speed) I got good results from a Solas Titan HR 4-blade stainless and I'm leaning in that direction again. They're good props and cost less than most.
So, do I drop an inch of pitch and keep my WOT around 4800 rpm, or do I keep the same (19) pitch and still be able to max out at around the middle of the recommended rpm range (I estimate 4600 rpm)?
Which do you think would give me the result I'm looking for (lower planing speed) in the mid-range??
Calm water and light breeze for a change, so I took her out for a top speed run. Wide open, both engines maxed out at 4800 rpm (top of the range) and I hit a top speed of 33+ knots/ 38-39 mph on GPS. That surprised me. I didn't expect her to be that fast. I seldom cruise at anything faster than 3600 rpm/26-27 mph. The water is normally too rough for comfort at higher speeds, so keep in mind that top speed is not my concern.
The issue - I can normally stay on plane down to about 20 mph/3100-3200 rpm. It's iffy below that, and I'll usually slowly 'fall off' If I drop the rpm's any lower. That's problematic when I convoy with friends that have larger inboard boats and cruise at around 18 mph. I'd like to be able to stay on plane at a couple mph slower than I can now. In those conditions, engine efficiency and mpg aren't my primary concerns- it's about staying with the group.
On a previous boat (same goal- lower planing speed) I got good results from a Solas Titan HR 4-blade stainless and I'm leaning in that direction again. They're good props and cost less than most.
So, do I drop an inch of pitch and keep my WOT around 4800 rpm, or do I keep the same (19) pitch and still be able to max out at around the middle of the recommended rpm range (I estimate 4600 rpm)?
Which do you think would give me the result I'm looking for (lower planing speed) in the mid-range??
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