prop sizing

[trincomali]

Does anyone have any advice for prop sizing for an Albin 25 with a Beta 35?

I'm currently seeing about 5kts in flat water at 1500rpm (which should be making about 16HP) or 7kts at 2300rpm (maybe 28HP).

That seems like a lot of power to me relative to what I'd expect from the Brohall handbook.

I actually don't know what kind of prop is on there right now, but I'm hauling her out next week and I'll find out, and wondering whether to be ready to swap it.

[ssrig]

That beta 35 is close to maybe what the boat came with? If it’s a Deluxe? 36hp.

If so then what you have on already could be a 17x 13 or 17x 14 and given what you see for speed I would say that is close to and is probably it’s optimal size. There most likely isn’t anything to be gained from changing it out, any speed above 6 knots is above hull speed.

I used a prop calculator that I got online from Victoria Prop so if you can locate that and input some data it will give you an approximate size for your boat.

[ssrig]

Here it is.
https://vicprop.com/displacement_size_new.php/?m=1

[DesertAlbin736]

Slight difference in hull design between early 1972 & older model full displacement hull "Albin 25" vs 1973 & later semi-displacemnent "Albin 25 deLuxe" variant. Former came OEM with Albin's own AD21, later with 36 HP Volvo MD3B & later MD17C. What we have is a 16 1/2 X 12 right hand prop for our 24 HP/2400 RPM continuous & 27HP/3600 RPM max for the Yanmar 3GM30F repower engine. Our theoretical full displacement hull speed in knots by formula = 1.34 X sq rt of waterline length in feet, which the A35 LWL = 22 ft, sq rt of 22 = 4.69 X 1.34 = 6.28 knots. The semi displacement deLuxe hull speed would be slightly higher, maybe an extra knot or two. We cruise +/- 6.5 knots GPS speed over ground in calm water running our 24 HP at 2,350 to 2,400 RPM.

20190715_190224.jpg

[SamNassar]

Hello all
A 25 1153
New to me
Boat has original LH propeller, no engine
Going to power with 3GM30, 3.2:1? Gear RH
Question, how do I remove the rudder to access the propeller?
Thanks Sam
Harpswell ME

[LydiaS]

Hi Sam,
On my A 25 # 1729 from November 1973, I found the shaft removed Forward, thru an existing hole in the main bulkhead; mine is a Deluxe, which may make a difference, but with no engine, this should be simpler than dropping the rudder.
Best of luck, from Camden

[WillieC]

You should have the handy dandy unique to A25s Special Purpose fitting at the connection between the skeg and the rudder shaft. Remove the bolt holding the fitting to the end of the skeg. The fitting looks like it is part of the skeg but it should separate, then drop off the end of the rudder shaft. If you have enough clearance and the tiller arm removed, the rudder will remove itself from its bushings and seals. As I recall you need about 30” from hull to ground to get it out. Bring shovel.

Now if yours has been modified, you are on your own. Good luck!

Sam, you need to introduce yourself so you can get a proper welcome here at AOG! Start a new thread. If you can figure that out, you’re hired!