Proper prop size tartan 33

[yawstick]

have tentatively agreed toto buy a 1980 Tartan 33... had the bottom cleaned and was advised there was no zinc on the prop shaft and the prop was in poor condition. I thought would know prop size but he does not. It has the 25 hp universal diesel engine... anyone have info on he prop size for this boat.

 

[Dave Groshong]

Most prop shops will ask the waterline length, max RPM's, max speed, transmission reduction ratio and engine brand/model

 

[capta]

Most prop manufacturers have a prop sizing guide on their web site. You will need some information, including the gear ratio of the transmission, which is very important. You may also be looking at replacing the shaft if it has been zinc-less for some time, so be prepared for a fairly large hit there.
The old prop should have its info punched into the hub and you could begin there, however, there is no guarantee that the former owner installed the correct prop, so be careful.

 

[yawstick]

I did find this... Prop Calculator

 

[Davidasailor26]

I did find this... Prop Calculator

Interesting calculator. I tried it with the numbers for my boat and it suggested 16x13 for 3 blades. Our fixed 3 blade prop from the factory was 17x12, and we’ve replaced it with a Flex-o-fold 16x12. Both of those behaved very well, easily reaching hull speed and being able to get maximum RPMs just below full fuel. So I’d say the calculator can get you close but might not be perfect depending on the exact prop model.

 

[jssailem]

Dave’s list

• waterline length,
• max RPM's,
• max speed,
• transmission reduction ratio
• and engine brand/model

is a a good start.
I like the information I found on the site WestbyNorth.

Considerations On Choosing A Sailboat Propeller - West By North

By Cliff FriesenThere are many old adages or beliefs about sailboat propellers that may have been true in their day. However, today most sailors sail differently from their predecessors. There are still the Lin & Larry Pardy types, engineless diehards that sail between anchorages, but they are...

westbynorth.com

It helped to better understand the issues associated with prop selection.
I inherited this prop on the boat


Working with a prop shop I installed this


Great improvement in engine performance and thrust. (1.5knots). Also a .9knot improvement in sailing

Seek out an expert over a catalog. I give high praise to WestbyNorth and their CampbellSailor prop design.

 

[yawstick]

Interesting... the top prop looks more like what you'd see on a correct craft instead of a sailboat... what's the numbers for them... diameter and pitch?

 

[jssailem]

I do not know the pitch. I can check the diameter. It is stored in my garage. I was thing of using it as a dinghy anchor.