Discussion in 'Precision Marine Center- Diesel & Propulsion' started by chasintail, Feb 6, 2017.
I have a 24 x21 prop on a 13/4 shaft if I went to a 24x24 what effect should that have ...... THANKS
at least a 300rpm loss, depending where you are now on the correct rpm scale.
I have a 24x25 or 26 4 blade nibral, Left hand, 1"3/4 shaft NIB
Bought for a project, wound up going w different motor
If your interested
iveco 270 hp 35 Bruno extended keel looking for more speed ........... so going to a24x 24 will bring 2900 rpm wide open down to 2600 it will make me slower ?
what should I go to for more speed ?
You should be thinking about engine health, more than speed. If you are at the upper end of of your engine HP at WOT, getting a prop with longer legs will not do anything for you but cost you money in engine repairs/life.
Best to run your numbers through a prop calculator or find someone who has a similar set up to compare (even then, its not the same). If you play around with props you may figure out where you are with engine loading.
What should be wide open throttle rpms be?
wide open in neutral is 2900 ....2950
I have no idea about isuzu engines, not familiar with them, need a model number. I believe it was meant as isuzu not iveco.
iveco 270 hp I get 20 knots wide open clean bottom run at about 2200 15, 16 knots with pulpit and crows nest on
my bad. What's your WOT RPM, in gear.
If you are running at the engine makers specified RPM at WOT with existing prop, and if existing prop has been checked & tuned; going for more pitch or diameter will just overload your engine. Going from 4 to 3 blades often results in slightly more speed IF the 3 blade has proper blade area to prevent cavitation. If not, you will loose speed. Occasionally a different brand or style propeller will produce slightly more speed.
Maybe shed some weight first as Bruno's are not the best weight carriers also have your tach checked to be sure what you are saying is actually true.
Finally, an unmodified 35 can really only handle a 22" prop as a 24 does not have enough clearance either above or below. I have always run a 22" on mine and picked up a full knot by dropping my skeg bar and shaft years ago, giving it proper room to work, fairing the deadwood didn't hurt either but I can't remember how much...
I modified it extended keel by about 6 or7 " shaft tube, dropped shaft,, longer rutter ,fairing some that's how I got to The 24 ....I could have a little capitation now looking at prop but not sure
so....like I said, I don't know the engine (or model #). But, if you are 2900-2950 in neutral (governor) and also hitting governor set point in gear and the specs for the engine support that, you may have some room to increase pitch. If you have the gear ratio, water line length and displacement I can run a prop calculator?
thank you , I don't know the displacement though , I had it figured when I put that motor in 4 yrs ago , and that's how I ended up with that 24 x21 ......
The most important factors are what is the engine supposed to reach at wot? and what is your gear ratio? Then what are you achieving with the existing prop which appears to be 2950rpm. Given all of that info you can be strafed in the right direction
Why don't you install a pyrometer in the exhaust manifold. Then you can monitor EGT's. As long as EGT's don't go too high at wot, you'll be fine with the bigger prop. Heck, I run a pyrometer in my 17 hp Lombardic Diesel powered Arctic Cat 700 ATV. I'm sure I'm the only one in the universe to have done that...
Really sorry I missed this thread, I have it set up so I get an email for the electronics posts, but not this one apparently. That said, it looks like you guys have already taken it to another level, and I'll be totally honest that this sht is WAY over my head, and my boss aka 'Greg Diesel' on the forum (although I don't think he knows how to post or has the time) is still in Islamorada fishing as we get the whole month of Feb. off for VaCa. We're back in the office on Monday, he's most likely going to have a pile of work to do but I'll fill him in and see if he as anything worth contributing. I will say I have actually learned a bit from this thread in particular, but I know that under/over propping is beyond any kind of exact science, but it's good to know once again the DEBF crew has it covered. Talk to you guys soon, I'm actually itching to get back to work, although by Monday afternoon I will regret even thinking that.
IF I GO FROM A 24 X 21 TO A 24 1/2 X 26 WHAT EFFECT WILL IT HAVE ? MORE SPEED OR MORE TORQUE ? THANK YOU