- Joined
- Sep 16, 2020
- Messages
- 59
- Reaction score
- 12
- Points
- 8
- Location
- Moosehead Lake, ME
- Model
- Adventure
Still planning my winter and spring projects for my new, old 208. I've been reading a lot of threads about Prop performance and engine RPM performance.
On my few runs after buying the boat and before winterizing I know I am getting low RPMs at WOT.
I knew this will obviously also give me slower speeds, but as I read more about props- if I'm doing my math right- my speed is way slower than it should be at the given RPM, meaning my "prop slip" is huge.
My prop is a stainless 14.25/17. The gear ratio of my Johnson 175 2s is 1.86. At 4300rpm I calculate that should give me a theoretical speed of about 37mph. I'm getting less than 25mph. That's a huge prop slip.
From what I read, many factors will negatively affect both rpm@WOT and prop slip.
For the sake of this post I'll ignore engine performance for 2 reasons. First, I leave those to my mechanic. I don't do engines (really wish I did, sometimes). Second, gaining 500rpm of WOT engine performance alone does little to affect my performance if I don't change the boat characteristics.
So, I plan to do the following as soon as I'm able:
1. Try a new prop. Even thought the prop looks OK, maybe it has a shape or hub issue. Easy enough to try a different prop. If possible, I'll try combinations of lower pitch (for more RPM), and wider diameter (for lower slip). Sounds like it's really trial and error to find the actual sweet spot. Obviously I'll get the best results if I can both increase RPM and reduce slip.
2. check the engine mount height. Just eyeballing the engine it seems to sit low. Once its out of the water I'll check the cavitation plate relative to the bottom. Maybe it needs to come up a peg or two.
3. Add trim tabs. I've read a bunch of pro/con posts here and on other forums. I'm strongly leaning toward adding them.
4. Clean the bottom as well as possible. There is little growth, but lots of rough, old layers of bottom paint. No one near me does soda blasting. I'll have to figure out my options in the spring.
5. I don't think I'm waterlogged. It's hard to evaluate the foam-filled hull sections. The parts I can see or reach are dry. I'll weigh the boat if I have a chance, but since this isn't a variable I can do much about, I'm focusing on everything else first.
Any other thoughts or suggestions? I'd love to hear that I'm missing something obvious.................. JB
Joe
Beaver Cove, ME
-
On my few runs after buying the boat and before winterizing I know I am getting low RPMs at WOT.
I knew this will obviously also give me slower speeds, but as I read more about props- if I'm doing my math right- my speed is way slower than it should be at the given RPM, meaning my "prop slip" is huge.
My prop is a stainless 14.25/17. The gear ratio of my Johnson 175 2s is 1.86. At 4300rpm I calculate that should give me a theoretical speed of about 37mph. I'm getting less than 25mph. That's a huge prop slip.
From what I read, many factors will negatively affect both rpm@WOT and prop slip.
For the sake of this post I'll ignore engine performance for 2 reasons. First, I leave those to my mechanic. I don't do engines (really wish I did, sometimes). Second, gaining 500rpm of WOT engine performance alone does little to affect my performance if I don't change the boat characteristics.
So, I plan to do the following as soon as I'm able:
1. Try a new prop. Even thought the prop looks OK, maybe it has a shape or hub issue. Easy enough to try a different prop. If possible, I'll try combinations of lower pitch (for more RPM), and wider diameter (for lower slip). Sounds like it's really trial and error to find the actual sweet spot. Obviously I'll get the best results if I can both increase RPM and reduce slip.
2. check the engine mount height. Just eyeballing the engine it seems to sit low. Once its out of the water I'll check the cavitation plate relative to the bottom. Maybe it needs to come up a peg or two.
3. Add trim tabs. I've read a bunch of pro/con posts here and on other forums. I'm strongly leaning toward adding them.
4. Clean the bottom as well as possible. There is little growth, but lots of rough, old layers of bottom paint. No one near me does soda blasting. I'll have to figure out my options in the spring.
5. I don't think I'm waterlogged. It's hard to evaluate the foam-filled hull sections. The parts I can see or reach are dry. I'll weigh the boat if I have a chance, but since this isn't a variable I can do much about, I'm focusing on everything else first.
Any other thoughts or suggestions? I'd love to hear that I'm missing something obvious.................. JB
Joe
Beaver Cove, ME
-
