| Author | Message | ||
     Scott Corder New member Username: Pastcommodore Post Number: 33 Registered: 02-2001 Rating: N/A |
George, (please forgive the length of my note) I read your last note re Yanmar conical clutches and props and agree with everything you've written, but have a question: You indicated that you changed prop pitch when changing props (gaining an extra knot under power). If you read a post I made much earlier in this same thread on the bulletin board, I mentioned some very strict advice I received from Martec concerning matching prop pitch to the gearbox on the engine. To reiterate: Martec was adamant that the prop be properly matched to each specific Yanmar gearbox to generate maximum thrust at approx 2900 rpm. Anything different and they said bad things could (would) happen (clutch burn out, engine damage, etc.) They also indicated that Yanmar shipped 2GMs with several different gearboxes on a totally unpredictable basis (just whatever gearbox they happened to have on the shelf as they made each engine). This, they said, obviously prevented them from providing any kind of widely applicable formula for prop size and pitch on a Yanmar 2GM. I have a HUGE (and subsequently heavy) hub on my prop (compared to most every other prop I've seen on a 9.1) and clearly have a different pitch on mine (hull 2) versus (for example) Greg Young's (hull 85). Years ago, when inquiring about these clutch and boat speed under power issues, I asked Martec about changing to a smaller hubbed prop that would generate more boat speed and they gave me the answer I just reiterated above. How did you manage to up-size without creating potential problems? I'm not totally unhappy with my speed under power, but hey an extra half knot makes a pretty huge difference when crossing 60-100 miles of Lake Michigan under power on a delivery! I've also posted or read related messages regarding the varying amounts of horsepower generated by different 2GM engines depending on their date of manufacture that may also play into the selection of appropriate prop pitch and resulting boat speed under power? Back to the example of comparing boat speed under power against Greg's hull 85 on all those cross-lake deliveries we've done together over the years: He just plain seems to have about a half to two-thirds of a knot more oomph under diesel than me. (and I know it isn't my bottom, which Gary's keel measuring report clearly confirms). Again, sorry about the long message here... I'm just VERY curious if I should be looking into swapping my prop for a lighter one (faster under sail) with a slightly different pitch that will make my little yacht also go faster under power? I reluctantly must admit that my sudden interest in speed under power is because these days I seem to spend much of my time on the boat with my 3 yr old twins who appear to love being on the boat but only for a couple of hours at a time. I'm very afraid they will melt-down if mom and dad actually try to accomplish a short weekend trip where it takes just a little too long to get there! Can you help a poor father out? p.s. Have a good time this weekend at the NOODS, we'll be thinking of you all and miss being there at the line with Scooter. |
