3 blade prop?

[P69]

Pete,

How do you get 17 x 10 on that prop calculator. I keep getting values that range from 15 x 9 to 15 x 8, depending on what I change, but never even close to what you are getting.

I have a 367 like Risto.  The motor in mine is the M50, 44hp, 3100max rpm.

here are the values I'm inputting:

lwl: 30
beam @ wl: 9
hull draft: 3
weight: 20000 (I also put 17000 an still got round 15 x 9 or so prop)
# engines: 1
hp: 44
max rpm: 3100 (I even tried 2300, but still got prop recommendations of 15 x n
gear ration: 1.9:1 (hurth ZF15, Walter RV20)
shaft bearings: 2 (shaft log and strut)
Desired speed: 7

I changed the values , but still the 3 blade prop recommendation was always around 14.9 to 15 x 8 or 9.

Thanks


Risto, when you get the prop worked out, let me know. I have a sistership (#42) and am looking for a 3 blade prop.

[PeteW]

I de-rated the M50 performance to 40HP at 2500 RPM (from the graph) and entered those as max HP and RPM. It spits out 17x13 with those numbers and specs 35HP to the water to achieve hull speed 7.3 Knots which shows that you have margin. And I assume the motor will be running slower at 2500 rpm. Which I think is preferable to flat out at 3000 rpm.

Gear ratio has to be 2:1 overall.  2:1 in the V-drive and 1:1 in gear box. A Hurth will not work in the Pearson 365 because you will be at 3.8:1 overall. 1.9x 2 = 3.8   With that gear ratio you need to swing a 27" x 21"inch prop which is impossible to do. Unless your RV26 has 1:1 gears in it meaning the repower was done right.

Pete

[P69]

Thanks Pete,

I double-checked and you are correct the v drive is a RV26 with a gear ratio of 1.00:1 (maybe, hard to read, waiting for feedback from Walter).

The ID plate on the hurth shows ZF15M for the model with the following ratios:  A=1.00 and B=1.95 (again, hard to read, but A value could be 1.88)

My mistake was that I was not reducing the rpm and hp correctly on the input table, giving me the odd prop values.

[PeteW]

Walter Machine documentation does not recommend putting the gear reduction in front of the V-drive. It has to do with the max HP rating of the drive that is reduced by the gear reduction. (torque increases) I don't have a spec sheet on the RV26 but the RV-20 1:1 specs out at 59HP at 1315 RPM (2500 at the motor) . So you should Ok there.

Where you are not OK is in the Hurth ZF15 which has become your weak link. Bad news is that at 2500 RPM the ZF15 continuous duty rating is 38 Hp. You might be inclined to call that good margin but in this case I am not going to recommend gearing up by going to a higher pitched prop. Without an oil cooler on the Hurth it will overheat and burn out. So stick with the lower pitch prop (17x 11) and rev your motor to 3000 rpm for hull speed. At 3000 rpm the Hurth ZF15 is rated for 46 hp. I've seen too many Hurth gearboxes burn out in a very short period of time.

It's too late for this but I would have kept the 2:1 v-drive, got rid of the  Hurth and put a Velvet Drive (direct drive) on the Universal motor. That's a 175 HP rated gearbox.

Meanwhile I'm very curious to see how you fitted an RV-26 into the Pearson 365.

[P69]

Here you go Pete, pictures as you requested.   

https://picasaweb.google.com/111274927949602013478/Vdrive#

Thanks for the info on which prop and the inadequacies of what I have.  It's good to know what to watch out for.


I don't know when the V drive was put in or if its install was at the same time as the Hurth. 
Wouldn't it be great of  the many POs of boats had done stuff right, instead of half-assed?  I guess that's one of the pitfalls of buying a used boat.   

So , if /when my hurth bites the dust, which velvet drive should I use. I then have to 1)confirm that my RV26 is 1:1 and 2) find out how much Walter charges to regear it to a 2:1. Of course, this is low priority because it's working and I 've got a long list of otherthings I'm working on, but it's good to have the info in my hip pocket so I can get to it when the failure occurs.

Thanks again Pete. Let me know if you want more details of my RV26 install.