Good morning all,
Quick introduction;
I'm located in Scituate which is just south of Boston in Massachusetts bay. I'm a new Grady White (and boat) owner. Just bought my 1983 20' boat last fall. It has what I believe is the original Mercruiser 470 (170hp) inboard/outboard engine. Overall boat and motor condition is what I would call "good", with some minor chips in the jell-coat and fading on the topside, but for 38 YO I think it's in great serviceable shape. I'll likely be posting some more questions but for now, I'm shopping for a new prop and would like to get some advice from others who have experience with a similar size/hp platform.
The current prop is a beat up 15x17 with a few chips taken out of it. It's what came with the boat. The motor WOT lists at 3800-4200 rpm. The boat gets on plane quickly and planes at about 15 knts I think. Cruises comfortably at 17kts at around 3500 rpm. At maximum rated rpm (4200) she hits 22-23 knots.
One issue is, there is still lots more throttle left. I don't know how much because I refuse to intentionally run it beyond the 4200 rpm spec.
Another issue may be that it's possibly cavitating at higher rpm? I don't know for sure, but it feels like if I advance the throttle at 3800-4000, that it spools up quite quickly.
So my question is; What prop size range do you think (from experience) works well with platform (20' walkaround and 170hp)? My thoughts are that the 15x17 is definitely under size and I was thinking of trying the 15x19 next. I'm sticking with aluminum for now to protect my outdrive, at least while I learn.
Hope this all makes sense and thanks in advance for the help,
Bob
Quick introduction;
I'm located in Scituate which is just south of Boston in Massachusetts bay. I'm a new Grady White (and boat) owner. Just bought my 1983 20' boat last fall. It has what I believe is the original Mercruiser 470 (170hp) inboard/outboard engine. Overall boat and motor condition is what I would call "good", with some minor chips in the jell-coat and fading on the topside, but for 38 YO I think it's in great serviceable shape. I'll likely be posting some more questions but for now, I'm shopping for a new prop and would like to get some advice from others who have experience with a similar size/hp platform.
The current prop is a beat up 15x17 with a few chips taken out of it. It's what came with the boat. The motor WOT lists at 3800-4200 rpm. The boat gets on plane quickly and planes at about 15 knts I think. Cruises comfortably at 17kts at around 3500 rpm. At maximum rated rpm (4200) she hits 22-23 knots.
One issue is, there is still lots more throttle left. I don't know how much because I refuse to intentionally run it beyond the 4200 rpm spec.
Another issue may be that it's possibly cavitating at higher rpm? I don't know for sure, but it feels like if I advance the throttle at 3800-4000, that it spools up quite quickly.
So my question is; What prop size range do you think (from experience) works well with platform (20' walkaround and 170hp)? My thoughts are that the 15x17 is definitely under size and I was thinking of trying the 15x19 next. I'm sticking with aluminum for now to protect my outdrive, at least while I learn.
Hope this all makes sense and thanks in advance for the help,
Bob