Prop sizing for Mainship???
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kapnd
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By all means, use a reputable prop shop.
They will provide you with a sheet with tons of questions, transmission ratio being one of them, so start digging in your files, and polishing up the tags for info.
Another hard but critical question is boat weight.
The OEM propellers are likely not what you will need, though it will give you some idea where to start.
Also make a chart of the performance with whatever props are on now, log engine rpm at 100 rev intervals across the range and plug in boat speed, engine and exhaust temp and manifold pressure if available. (With clean bottom and running gear)
Check to make sure the engine is capable of making rated rpm in neutral.
If it won't, fix it before attempting to select new props.
This will all help your prop shop select the right prop for your rig.
If you'd like to understand more on the subject, I would suggest reading Dave Gerrs "Propeller Handbook".
They will provide you with a sheet with tons of questions, transmission ratio being one of them, so start digging in your files, and polishing up the tags for info.
Another hard but critical question is boat weight.
The OEM propellers are likely not what you will need, though it will give you some idea where to start.
Also make a chart of the performance with whatever props are on now, log engine rpm at 100 rev intervals across the range and plug in boat speed, engine and exhaust temp and manifold pressure if available. (With clean bottom and running gear)
Check to make sure the engine is capable of making rated rpm in neutral.
If it won't, fix it before attempting to select new props.
This will all help your prop shop select the right prop for your rig.
If you'd like to understand more on the subject, I would suggest reading Dave Gerrs "Propeller Handbook".
C lectric
Guru
I will add, strongly, to get a laser pointer digital photo tachometer for less than $50.00
on E bay. Put a piece of the reflective tape on crankshaft damper use the phototachs to check the revs.
Cheap as they are they are far more accurate than typical dash tachs which are often seen to be wrong by up to 200 revs. You will need good rev info to get good prop work/recommendations.
on E bay. Put a piece of the reflective tape on crankshaft damper use the phototachs to check the revs.
Cheap as they are they are far more accurate than typical dash tachs which are often seen to be wrong by up to 200 revs. You will need good rev info to get good prop work/recommendations.
PMF1984
Guru
You might find your transmission info in the boat survey(if you had one done)
A little far for you, but I use Scandia in Fairhaven, MA
A little far for you, but I use Scandia in Fairhaven, MA
PMF1984
Guru
You have to get the transmission info on the transmission plate.
Think about the work the engine does and about how it relates to the transmission.
The work the engine does relates to the rpm, transmission, prop diameter and pitch.
The work the engine should do is related to type of hull, length, beam, and tonnage.
I the "does" is more than "should do" you'll be seeing black smoke soon (if you have a diesel) that's a sign of asking too muck work from the engine
Most prop places have a computer program now that needs these inputs.
Think about the work the engine does and about how it relates to the transmission.
The work the engine does relates to the rpm, transmission, prop diameter and pitch.
The work the engine should do is related to type of hull, length, beam, and tonnage.
I the "does" is more than "should do" you'll be seeing black smoke soon (if you have a diesel) that's a sign of asking too muck work from the engine
Most prop places have a computer program now that needs these inputs.
Pmcsurf1
Senior Member
If I switch from a 5 blade 26x19.5 to a 4 blade what would the 4 blade pitch be too equal the 5 blade?
