Propeller optimalisation choice?

G

glljansen

New Member
Joined
21 Feb 2009
Messages
6
Visit site
What propeller to optimize speed for Mitchell Sea Angler 31ft with Perkins Sabre MTI300 (300HP)?
Any suggestions on what speed to reach under ideal conditions?
Rgds
Guido
 
glljansen said:
What propeller to optimize speed for Mitchell Sea Angler 31ft with Perkins Sabre MTI300 (300HP)?
Any suggestions on what speed to reach under ideal conditions?
Rgds
Guido
Click to expand...

Only wild assed guess with current information, however if I assume 4.25 tonnes 29 ft LWL with 1.5:1 transmission.

Perkins Sabre 300 is 300 in name only as they used outdated BS AU 141A and the magic words 'maximum potential power' actual power for use in calculation should be 275 hp and assuming ability to swing 21inch wheel a four blade 21X21 propeller sounds about right giving tad under 23 knots @ WOT and cruise of 20 knots 200 rpm off the top.
 
glljansen said:
Thank you; this brings us closer.. transmission however is 1.2:1.
Click to expand...

Mmmm, 21 inch diameter wheel a little near the knuckle with 1.2:1 reduction. IF you are on 21 inch diameter pitch would need to come down nearer 14 inches. However 19X17 or perhaps 16.5 may be tad better than 21 as tip speed is getting critical with 1.2:1
 
Sorry, after recheck, the transmission is 1.533:1
So Thanks again, we will give feedback after overhaul of the boat.
Guido
 
Latestarter1 said:
Product of artificial intelligence.........Simply a trusty slide rule!
Click to expand...
LOL, really? That must be some slide rule indeed.
When I visited the Kennedy Space Center in Cape Canaveral, they showed us a slide rule that was used back in the days of the first moon landing.
I bet yours is more sophisticated! :D
 
MapisM said:
LOL, really? That must be some slide rule indeed.
When I visited the Kennedy Space Center in Cape Canaveral, they showed us a slide rule that was used back in the days of the first moon landing.
I bet yours is more sophisticated! :D
Click to expand...

In the 1970's Cummins produced a slide rule to calculate geared speeds, power demand, etc etc for use when specifying engine gearbox axle configurations and another for marine engine gearbox prop calculations. Limited range of SD factors but real use when making quick and dirty estimates on the fly, Cat produced something very similar, as well as a brilliant tool called the Caterpiller pitchometer for determining prop pitch.

Americans loved these toys and I inherited both calculators in the 80's when everybody thought computers were the hot thing and this stuff old hat. I guard these with my life, along with my U.S. Hydrographic Office Rude Star Identifier, probably the best navigation aid ever identified! Using the star identifier I can pre determine altitude and bearing find a star and bang off sight reduction at twilight levels where horizon is still sharp.
 
Amazing stuff indeed.
I wish I had one of those star identifiers onboard, just to pretend to be able to do the same and impress visiting friends.... :D :p :D
 
Thanks, I'll get one.
Not that I'm thinking to actually use it, but I've already got a sextant onboard, and this thingie will make for a perfect match! :D
 
You must log in or register to reply here.

Other threads that may be of interest

boatmike
Merry Fisher 695
Replies
3
Views
264
Bouba
Bouba

Share this page

Top