best propeller pitch
 

I have an Albin 27 family Crusier with a lehman 4d61 diesel in it. This
boat is only able to get up to 8 knts. I have heard of others getting
10 to 11 knts with the 61 hp diesel. Does anyone have this boat or info
as to what the optimun pitch might be I have a 3 bladed 19" prop.
Thanks, Paul

any prop shop can help you. There is a formula they use that I do not
know. Sometimes they have your hull dialed in already but other times
they will need LOA, BAW, Real weight (not what the factory says but
after all your stuff is in it) and a few other numbers.

When I repowered, I repitched my prop after about 100 hours of useing
the original. The change of a little bit (something like 1.5) made a
400 rpm drop for speed so it is worth doing.

Paul:

I plugged the following info on your boat into the prop calculator at
boatdiesel.com (you have to pay $25 for a year's membership to use it):
7,000 lb displacement, 25' LWL, fast semi-displacment hull, 2:1 transmission
ratio, 19" prop, 61 hp diesel. The calculator shows a maximum speed of 10.9
kts and a 20" pitch prop required. I also ran 8,000 lbs in case you have
loaded her up a bit (Yachtworld lists several Albin 27s at 6,500 lb
displacement, but that is usually dry) and got 10.4 kts and also 20" pitch.

The first question to ask yourself re pitch and WOT speed is does the engine
reach rated rpm (or a bit more) at WOT. If not you could be overpitched,
have a fouled prop or bottom. I would doubt that the manufacurer would have
missed the pitch that bad, so look at the other two causes first. The engine
may also be a problem, but I would rule out the others first.

David

"boater435" wrote in message
oups.com...
I have an Albin 27 family Crusier with a lehman 4d61 diesel in it. This
boat is only able to get up to 8 knts. I have heard of others getting
10 to 11 knts with the 61 hp diesel. Does anyone have this boat or info
as to what the optimun pitch might be I have a 3 bladed 19" prop.
Thanks, Paul

In article k0_Se.74073$DW1.692@fed1read06,
"David&Joan" wrote:

The first question to ask yourself re pitch and WOT speed is does the engine
reach rated rpm (or a bit more) at WOT. If not you could be overpitched,
have a fouled prop or bottom. I would doubt that the manufacurer would have
missed the pitch that bad, so look at the other two causes first. The engine
may also be a problem, but I would rule out the others first.

Don't rule out being mis-propped by the manufacturer as they might not
have gotten exactly what they ordered from their supplier. Our pretty
nearly new fixed 2 blade Michigan Wheel's blades had an inch different
pitch between them, and neither was what was marked. Balancing the prop
improved performance and greatly decreased vibration.

--
Jere Lull
Xan-a-Deux ('73 Tanzer 28 #4 out of Tolchester, MD)
Xan's Pages: http://members.dca.net/jerelull/X-Main.html
Our BVI FAQs (290+ pics) http://homepage.mac.com/jerelull/BVI/