MaxProp in CD36

[Troy Scott]

Folks, especially Bill Cochrane,

I want to install my 15" MaxProp on my CD36 with Perkins 4.108. The boat now sports a standard solid three blade 15-14 prop, which I hope to finish pulling off today. In an old post Bill talked about having to experiment with the MaxProp on his CD36 to find the best pitch. I believe I remember he started out at 13.8 and ended up at 11. First, I'm unsure about blade angle vs another style of description which indicates how far the prop would theoretically travel in one revolution if it didn't slip, which it does.... I'm sure I can measure the actual angle of the old prop pretty close with a protractor. The MaxProp irections suggest starting out with the same angle as the original prop. However, I see that the MaxProp has 5.5" wide blades as compared to the 4" wide blades on the original. There is MUCH more blade area on the MaxProp. Maybe this is the reason Bill ended up with a flatter angle? I would appreciate and advice on setting up the new prop. I don't want to go through a long process of trying various angles if I can benefit from the experience of others wth this engine/prop combination.

[Bill Cochrane]

You've summarized my conclusion, although proper pitch is a bit of art and black magic in addition to science...I'm beginning to think I could take even a bit more pitch out of the prop.

You should be able to hit hull speed, with a clean bottom, no wind/waves to slow you down, at or not too far below the rated top end of your engine. IIRC, Perkins specs 3 top end speeds depending on use, and the most conservative is 2600 (I think the others were 3000 and 3600, but I'm doing this from memory).

If you get black smoke and engine overheating during that test, you've got too much pitch. If you can't get to hull speed, and the engine is not pouring out black smoke, you haven't got enough pitch.

If I recall correctly, those of us who have repitiched the CD36 3 blade have all ended up at about 11-12" pitch.

[Troy Scott]

Bill,

Thanks for responding so quickly!
I'm still confused by the inches vs degrees thing and how to convert. My Max Prop manual only refers to degrees.

[Bill Cochrane]

Check the first two tables on this web page for the three blade max prop:

http://www.pyiinc.com/index.php?section ... ation&sn=3

Degree/pitch relationship changes according to diameter; you set the prop in degrees, but it converts to a pitch setting.

[Russell]

I had considered putting on a maxprop on my CD36, but after some measurement I concluded it would not fit in the existing space without rudder modification. Was I incorrect? Or did you have to do some modification to make it fit?

[Troy Scott]

Well, it must have fit on Bill Cochrane's 36; he didn't mention any alterations. It sure LOOKS like it would fit. If it doesn't I'll just put it back in the box.

Right now my problem is getting the old prop OFF. I've soaked the whole mess in PB Blaster for two days. I've used three different gear pullers..., the last supposedly a "10 ton" tool. I broke a high quality wrench tensioning the puller, and the prop is still firmly on there. My next attempt will add chilling the shaft while heating the prop. We'll see......

[Bill Cochrane]

...but the PO had the installation done.

There was some correspondence onboard indicating that perhaps the installation was not straightforward, but unfortunately there were very few details; the manufacturer (PYI) indicated in a letter to the PO that the prop had previously been fitted to CD36's without problem but that changes in production boats did occur; they offered to take back the prop if (unspecified) modifications were unacceptable. A call or email to PYI may help (or may not...??)

The shaft was changed at some point as the one now fitted is stainless and the original was bronze.

Here's a shot showing clearances. I believe the top blade is close to vertical so the bottom clearance appears greater than actual.

This is the 15" original 3-blade model.

The prop is almost against the fitting on the hull (about 1/2" clearance or so) so the shaft may have been shortened, but I really don't know what was done.

Regards, Bill

[Troy Scott]

Bill,

I believe the photo shows some alteration to the rudder. I'll take the photo to the boat tomorrow for comparison.

Folks,

Is there another folding or feathering prop that will fit the 36 WITHOUT alterations?

BTW, I DID get the old prop off today.

[Parfait's Provider]

I am pretty certain Parfait's rudder doesn't have that bite near the prop. I'll check the photos and post again if I am wrong.

[David van den Burgh]

...
<img width="540" src="http://i52.photobucket.com/albums/g37/wmcochr/prop.jpg">

Here's a picture of Ariel's aperture for comparison. (Sorry I can't find a prettier picture.)

[Bill Cochrane]

David, thanks for the pic. Looks like the rudder was nibbled a bit to allow aft clearance. The things you learn on this board...

Anyone out there who went through the MaxProp install on a CD36 and can shed some more light?

[Troy Scott]

Bill,

Apparently someone has removed about an inch of material from the leading edge of your rudder in way of the prop. The question NOW is whether this rudder change was actually necessary or just optional. Dave Perry told me RMC has installed several Max Props on Robinhood 36s, but he did NOT mention any rudder modifications.

[Tom Keevil]

We went through this with our CD33. We intended to put a Max Prop on, but found it wouldn't fit. We determined that by comparing the specifications from the Max Prop folks to the measurements of our aperture (the boat was on the hard at the time). I don't have the data here, but I'm sure you can get it from them. It had to do with how much room was available aft of the shaft. It has a longer hub than the normal prop.

[patturner]

I looked into putting a MaxProp on my CD36. Couldn't do it without mofidifications and I'm pretty sure that applies to all the CD36's out there. You might look into the Variprop http://www.varipropusa.com/.
It has the shortest hub of all the feathering props out there and I know it will fit. You candownload a template that allows you to check the fit befor purchasing. I did just that and looked like no problem. The model that was recommended to me was the DF-107. I have not gone through with the purchase - ran out of money, but that is the one I would choose.

Pat
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Mazda 767 History
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NO2 VAPORIZERS

[Troy Scott]

Folks,

As part of my investigation, I partially installed my Max Prop on my CD36. I took it far enough to determine that the blades when feathered would try to occupy the same space as the forward 3/8" (not exact) of the rudder. Also, the zinc nut/fairing on the trailing edge runs into the rudder, but only slightly. In short, the rudder MUST BE MODIFIED like Bill Cochrane's rudder in order to install and use the Max Prop on a CD36.