davlafont
Cadet
- Joined
- Jun 18, 2010
- Messages
- 28
Q: What conditions would warrant one gear ratio over the other? Or put another way, what might cause a shop to use a certain ratio when assembling a boat for sale (1.47 vs. 1.62 vs. 1.81)?
This question is more for my own education than it is for solving a problem. I don?t know what ratio we have (I?m working to get that info) and before I replace the current 14.5 x 21P prop, I want to make sure it has any business being there in the first place. According to the Merc Prop Selection Tool/site, no combination of conditions/answers for the 1.47 or 1.62 ratios leads to a 21P recommendation. Under certain conditions, 21P could be appropriate for the 1.81 ratio.
Background:
Our prop is chewed up and we plan to replace it with a like prop before beginning the process of ?dialing in? what prop suits our needs; I want to start with a fresh prop as the boat was delivered and baseline its performance. But based on the boat?s behavior last weekend, it very much feels overpropped for skiing and towing with the whole family aboard and a cooler full of beverages. (It doesn?t help matters that the tach is suddenly not working. Of course... that?s because I had planned to make note of the RPMs at WOT).
So I?m curious about gear ratio theory because I know no one here can tell me what I have (I have my 75-year old dad getting into the water two states away to look at the outdrive and attempt to find the ratio marking). But if anyone can tell me what the common practices are regarding how these powertrains are assembled, it might help me better understand why there is a 14.5 x 21P prop on there now.
Boat details:
2003 Bayliner 205BR
Merc 5.0 liter carbureted V8
Merc Alpha one sterndrive, gear ratio unknown!, 14.5 x 21P 3-blade alu prop
This question is more for my own education than it is for solving a problem. I don?t know what ratio we have (I?m working to get that info) and before I replace the current 14.5 x 21P prop, I want to make sure it has any business being there in the first place. According to the Merc Prop Selection Tool/site, no combination of conditions/answers for the 1.47 or 1.62 ratios leads to a 21P recommendation. Under certain conditions, 21P could be appropriate for the 1.81 ratio.
Background:
Our prop is chewed up and we plan to replace it with a like prop before beginning the process of ?dialing in? what prop suits our needs; I want to start with a fresh prop as the boat was delivered and baseline its performance. But based on the boat?s behavior last weekend, it very much feels overpropped for skiing and towing with the whole family aboard and a cooler full of beverages. (It doesn?t help matters that the tach is suddenly not working. Of course... that?s because I had planned to make note of the RPMs at WOT).
So I?m curious about gear ratio theory because I know no one here can tell me what I have (I have my 75-year old dad getting into the water two states away to look at the outdrive and attempt to find the ratio marking). But if anyone can tell me what the common practices are regarding how these powertrains are assembled, it might help me better understand why there is a 14.5 x 21P prop on there now.
Boat details:
2003 Bayliner 205BR
Merc 5.0 liter carbureted V8
Merc Alpha one sterndrive, gear ratio unknown!, 14.5 x 21P 3-blade alu prop
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