pcrussell50
Petty Officer 1st Class
- Joined
- Sep 21, 2008
- Messages
- 296
back around the beginning of the year, i launched a thread about how deep to run my 1975 v4 crossflow, 135hp, on it's light 16 footer, sport hull. turns out i had been running it too deep. there is a plate above the anti-cav plate that i learned was there for spray control. i had my motor set so THAT plate was just skimming the surface. now i have it so the anti-cav plate is just skimming the surface. whew...
but the thread morphed into the fact that my boat was only GPS'ing about 40mph, [sometimes a little more, sometimes a little less, depending on the prop], at an indicated 6000rpm and i was having to throttle back to keep it there. but the math simply was not adding up. there was no way this light little boat was getting 35-40% prop slip with the OMC raker series props i was using.
i'd been baffled by the whole year i owned the boat, until the fateful post by iboats luminary, dhadley. it just HAD to be the tach. you all said that my v4 crossflow, despite being a 4-cylinder motor, has six tach pickups under the flywheel, and therefore the tach has to be set on position 6. well, sure enough, my tach was NOT set on 6. in fact, it does not even _have_ a position 6. it just has 1-4. this is both a
and a
so today, i threw on a 22 pitch omc raker and put just myself in the boat, inaccurate tach, and all, and for the first time since i bought this boat a year and a half ago, i opened the throttle up all the way. this time, each time i started to get to about 52mph, it would juuust start chine walking, and i would back off for fear of it becoming divergent, as i have not developed the skills to drive a boat with the performance to chine walk. not to mention all the setup issues that come with it.
anyway, i'm glad i found my missing performance, even if i can't or shouldn't go there yet.
-peter
but the thread morphed into the fact that my boat was only GPS'ing about 40mph, [sometimes a little more, sometimes a little less, depending on the prop], at an indicated 6000rpm and i was having to throttle back to keep it there. but the math simply was not adding up. there was no way this light little boat was getting 35-40% prop slip with the OMC raker series props i was using.
i'd been baffled by the whole year i owned the boat, until the fateful post by iboats luminary, dhadley. it just HAD to be the tach. you all said that my v4 crossflow, despite being a 4-cylinder motor, has six tach pickups under the flywheel, and therefore the tach has to be set on position 6. well, sure enough, my tach was NOT set on 6. in fact, it does not even _have_ a position 6. it just has 1-4. this is both a
and a so today, i threw on a 22 pitch omc raker and put just myself in the boat, inaccurate tach, and all, and for the first time since i bought this boat a year and a half ago, i opened the throttle up all the way. this time, each time i started to get to about 52mph, it would juuust start chine walking, and i would back off for fear of it becoming divergent, as i have not developed the skills to drive a boat with the performance to chine walk. not to mention all the setup issues that come with it.
anyway, i'm glad i found my missing performance, even if i can't or shouldn't go there yet.
-peter