Originally Posted by Gelfling
I have searched the forum and have not found a situation like mine. It does appear that once a boat has had a certain number of owners for a certain number of years....no matter how well maintained the boat....there are parts
that just don't match up!
My question has to do with the prop. My boat came stocked with a Universal M-15 (5411, 11hp), but has been upgraded to a M-18 (14hp). The previous owner told me that he did not change the prop when he upgraded the engine and after research
it appears the manufacturer calls for the same size prop for both engines. With that said, I need a new prop and would like to go to a 3 blade
as it now has a 2 blade
. As we do a bit of gunk-holing I have found that having that extra under power is more beneficial than what I loose under sail.
The 'kicker' is, the current
blade is stamped: 2X12RH (maybe a '1' at the beginning has been worn off??) and the manufacturer suggests a 13X10. I am not a 'prop guy' by any means....so what am I to make of this?
Now, I could use the MFG specs and calculate from there, but there seems to be so many 'generics' out there about how to size from a 2 blade
to a 3 blade. How would I make the conversion so that I can maximize my speed under power?
You know my engine. Here is the boat: ERICSON 28+ sailboat specifications and details on sailboatdata.com
Any help would be greatly appreciated!
Why not try an online propeller calculator? Castle Marine
of the UK do one but unfortunately if you have had Windows 7 64 bit foisted upon you after being burgled, the Castle Marine
programme will not work as it runs 16 bit code. It used to run perfectly with Windows XP 32 bit but Windows 7 Home Premium is no good unless one pays a large fee for the XP downgrade.
One programme that does work is by Vicprop of Canada
One problem you may find is that your boat might be MUCH heavier than what is posted on the web. Examine the hull
very carefully for signs of the original bootop hidden under the paint
and check to see whether extra ballast has been added. I did have the misfortune to get sweet-talked into moving a boat for a friend a while ago and in spite of THREE surveys in the boats log book no one had noticed the two tons of extra ballast. Later it was noticed that the original bootop was hidden under the paint
seven inches lower down. Luckily the additional weight was no problem at all for my Land Rover.
Vicprop - Propeller Calculator
It is important not to be over-propped as this will cause the engine to make black smoke. Eventually the cylinder head
will get choked with carbon if things are left like this. Yanmar
will not guarantee their engines unless a sea-trial is done which shows that the engine can reach its maximum revs.
Note that marine growths on the prop such as barnacles
will also cause black smoke so it is advisable to be slightly under-propped to allow for the times when the propeller will not have a mirror finish.