A25 inner shaft bearing

[dkirsop]

If I had to reposer again I would use the spare AD21 sitting in my workshop. A man can't have too many spare engines!

[Desertboater]

We have been very pleased with the Beta 25. It is a good match for the AD21 that these early boats were designed for. The key elements for us were the weight savings and the physical size envelope of the Beta 25. No modifications of the engine box were required for the installation.

As is typical for the early full displacement A25, full throttle digs the stern in and raises the bow with only a slight increase in speed. Fuel consumption certainly increases!

Additional horsepower theoretically would overcome air drag forces due to high wind coming from ahead.

We typically cruise at 2500 rpm which is about the peak of the torque curve for the Beta 25. At this rpm, the engine produces 16.5 horsepower (ISO 8565 curve, not max output curve). Per the same engine performance graphic, 3600 rpm would produce about 22 HP.

As an example of how to calculate the effect of wind, the following web site has a calculation for 90 kph wind (50 mph) wind drag on a car. There is clearly a major difference between a boat that is designed to 'cut' through water (and also air) and a car, but the calculation provides some insight.

https://www.engineeringtoolbox.com/drag ... d_627.html

The result is 5.4 kilowatts or 7.3 horsepower is required to overcome the wind drag for a car like a Honda Accord.

This type of calculation essentially provides the engineering basis for our real world observation that we can maintain the same cruising speed into the wind as the wind increases by advancing the throttle. Long before the wind gets strong enough that our speed starts to decease, the waves get so high that we have no interest in being out in such rough water.

[honza]

Desertboater, what are the propeller parameters of this one, you use with the Beta 25? Would you change anything? What is your speed at 2500 rpm, if no wind, no current and flat waters? Thank you.

As for the wind - my other boat is Farrier 9R trimaran. I do not have an anchor winch on it and pull the anchor by hand single handed often. When it is windy I use my high trust Yamaha 9.9 (10 in. prop?) to keep the boat from drifting and pulling on the anchor rode. It takes just a higher idle (less than 2HP??), to keep the boat in neutral position at 20 kn wind, measured by wind instruments. I think, that the tri with cross beams, floats and a wing mast has much higher drag, than A 25. BTW, the Yamaha has a bollard pull at full rpm pulsating between 180 - 220 lb. In my opinion, at boat speeds of our magnitude, bollard pull is much better indicator of strong head wind performance potential, than horse power.

[honza]

One more question. Is your transmission TMC 40 with 2.6:1 gearing? Thank you.

[DesertAlbin736]

Desertboater (they call me DA for short, shall we call you DB?), nice analysis. Power wise the Beta 25 is similar to our Yanmar 3GM30F. We normally cruise at 2350 RPM (2.61:1 trans) turning a 16 1/2 X 12 prop. In still water & light wind that gives us GPS speed of 6.4 to 6.5 kts.

[Desertboater]

Sorry for the late reply but we were on a long planned vacation in Australia and not accessing the internet. Then after our sooner than planned return, the CPU in the PC fried. Anyway, back on line now.

honza - I agree that bollard pull would be a great way to see what the forces are at different engine RPMs. Then you could calculate the drag force on the Albin due to wind at different wind speed and determine how strong a wind you could sustain and still maintain cruising speed.

You asked about the propeller - I do not have the paper work but it is a Michigan wheel 3 blade Dyna Jet for a 1 inch shaft. The prop was sized to meet the clearances recommended by Michigan Wheel from the hull to prop and lower rudder support to prop.

This is the one part of our re-power that I did not procure directly. Shaft, coupling, and prop were purchased thru Inland Marine in Portland. They did the machining of the shaft and lapped the prop to the shaft. I believe they used the prop calculator on the Michigan Wheel web page to select diameter & pitch.

Speed question - since we usually are in the Columbia River, I make a run upstream & then downstream, then let the boat drift, then average out the two runs and allow for current. Since the runs are a mile of so, the river conditions can vary. So needless to say there is some uncertainty in the final numbers.

2600 to 2700 rpm results in about 6.7 knots. Full throttle might gain another .3 to .5 knots but the bow rises a lot.

Transmission is a TMC 40 with 2.6:1 ratio.

DesertAlbin - you suggested DB as a handle. Good idea, thanks

[honza]

Thanks, Desertboater, welcome back.
My interest with the bollard pull comes from a few situations, where I had plenty of power (HP), but could not make any progress into head winds, because the prop was slipping 100%. Bollard pull is defined as a force (pull on the line) while stationary and tied to a bollard, in enough water under the prop, that it does not impact its function (the flow). It should give some indication in how strong wind (in flat water) you would be able to make headway. My guess for the A25 with 11.5 in prop is about 400-500 lb. Hope to find time and a solid dock to measure it this summer. It also gives some indication about how good is the match of your prop (diameter, pitch) to your HP, RPM etc.

[WillieC]

"but the bow rises a lot."

Thus the deLuxe recurve. Very interesting.

[DesertAlbin736]

DesertAlbin - you suggested DB as a handle. Good idea, thanks

You're quite welcome, & welcome back from Down Under.

That makes three 1971's active on AOG, some of the oldest A25's around, tribologist/hull #737, dkirsop/hull#1013, myself/hull #736.

What's your hull # DB?

Speed wise we're a pretty good comp & comparison between Yanmar & Beta. I run 6.5kts @ 2,350 RPM, 2.6:1 gear ratio, 24 HP, 16.5x12
prop. I have a scant inch or so clearance between prop & rudder skeg. She runs smooth as glass & quiet as a mouse.

DSCN3631crop.jpg

[WillieC]

Sounds like mine. With the engine off.