utskicat
Seaman Apprentice
- Joined
- Dec 15, 2015
- Messages
- 41
I have a 1975 Fiberform 19' fibreglass ski boat. It has an interesting history. Originally, it had a Mercruiser 888 drive (MC-1drive mated to a Ford 302 2bbl block, 188hp, 1.50 gear ratio). When that engine was used up, it was repowered with a 351w with 4bbl Edelbrock 1409 (approx 260hp). That was a few years ago and has never been used since it got the new engine.
I inherited her and got her cleaned up and did a good service on the leg this winter (bellows, bearing, pump, gear oil, etc). My uncle (previous owner) thinks the old prop is now way under propped for the 351w.
Prop is a 3 blade aluminum 14.5x17p.
The boat is a big old fiberglass ski boat with deep-v hull. Weight with engine is about 3000 lbs.
Out on the water, she pops up on plane with hardly any throttle at all. The tach goes up to 6000+ rpm and 35mph at about 3/4 of WOT. The engine doesn't sound like its redlining, she just purrs away, but I have been too concerned about the rpm's on the tach to open her up anymore.
So so my question is two-fold:
1) Both engines were V8's so the old tach should work fine with new engine, right? Is it possible my tach is just way off? For the 351w, I should be at 4200-4800 rpm's from my research. If I am so under propped that the tach is actually correct, I would need a massive gain in pitch size to bring the rpm's down into range based on 1" gain = 200 rpm drop, right?
2) Using Merc prop tool it (used 5.7 engine, it doesn't have any choices older than year 2000), it recommends anywhere from 19-21" pitch. What do you guys say? And should I consider 4 blade? We will use it as a family boat with occasional skier/wakeboard (more as the kids 2 and 4 yr old get older).
3) Original 302 engine and drive were 1.50 gear ratio. The 351w was used in same time frame on Merc 233 with a 1.32:1 gear ratio. The 888 1.50:1 leg I'm using with the 351w should still be fine, right?
I inherited her and got her cleaned up and did a good service on the leg this winter (bellows, bearing, pump, gear oil, etc). My uncle (previous owner) thinks the old prop is now way under propped for the 351w.
Prop is a 3 blade aluminum 14.5x17p.
The boat is a big old fiberglass ski boat with deep-v hull. Weight with engine is about 3000 lbs.
Out on the water, she pops up on plane with hardly any throttle at all. The tach goes up to 6000+ rpm and 35mph at about 3/4 of WOT. The engine doesn't sound like its redlining, she just purrs away, but I have been too concerned about the rpm's on the tach to open her up anymore.
So so my question is two-fold:
1) Both engines were V8's so the old tach should work fine with new engine, right? Is it possible my tach is just way off? For the 351w, I should be at 4200-4800 rpm's from my research. If I am so under propped that the tach is actually correct, I would need a massive gain in pitch size to bring the rpm's down into range based on 1" gain = 200 rpm drop, right?
2) Using Merc prop tool it (used 5.7 engine, it doesn't have any choices older than year 2000), it recommends anywhere from 19-21" pitch. What do you guys say? And should I consider 4 blade? We will use it as a family boat with occasional skier/wakeboard (more as the kids 2 and 4 yr old get older).
3) Original 302 engine and drive were 1.50 gear ratio. The 351w was used in same time frame on Merc 233 with a 1.32:1 gear ratio. The 888 1.50:1 leg I'm using with the 351w should still be fine, right?