Fixed Vs. folding 3 blade propeller for Cal 39 MK2

[epoxyman]

Hello all - Maybe someone can help with this.
I have a 2 bladed MaxProp classic feathering prop (17 in. 16 deg 1.25 in shaft) that doesn't push the boat near hull speed (maybe get 6 knots at 2800 rpm)
Flexofold recommends a 3 blade 18 in. by 14 deg. right handed prop = but it may be too expensive for me this year.
I have access to a 18 in. 22 deg pitched right handed prop that is fixed blade, but I do not know if it will do what I need it to do (I realize I will give up sailing speed, but I need the push when the weather or tide is an issue).
Will a 22 degree pitch work for the Cal 39???
I have a 55 hp Yanmar 4JH4E, 5.5 ft draft, and gear ratio of 1:3.26.
Can anyone out there give me perspective on the fixed pitch Vs. folding or feathering? And what I should be looking for with a fixed 3 bladed prop
Thanks

[DougR]

Couple of questions:
- is the gear ratio really 3.26:1 ? That's an unusual ratio.
- do you mean that the pitch of your fixed blade prop is 22 INCHES? as opposed to degrees.

Confirm the ratio and pitch and I can run the numbers for you.

DougR

[Cheechako]

You dont need a fixed prop. I far prefer feathering. But if your Max Prop isn't reaching hull speed then you need to adjust pitch, clean your hull or something else. I've had 5 Max Props in my time and all had no problem with hull speed. My 44 ft boat reached speed easily with a 17 inch max prop, and not much more HP than your 39 ft boat.
Your Max prop should reach hull speed with no problem
You have enough HP.

Key question:What rpm does the engine reach wide open?

[epoxyman]

Hi Doug
You are right I had a senior moment - ratio is 2.36:1

the maxprop is 17 in 16 deg pitch right hand rotation

The fixed prop that I am looking at is 18 in diam. 22 pitch right hand

The major issue with the classic 2 blade feathering prop may be that in most cases you need to hacksaw off the end of the shaft which would be the last threads and the cotter pin hole. I have not verified this with my shaft (need to disassemble the prop) but the videos I have seen on youtube and the manual for the 2 blade classic all show this. This basically will screw me for all replacement props - I have an email into DYI to see if their 3 blade classic will interchange. Otherwise I will have to replace the shaft too.-- NOT an easy job

[Cheechako]

Originally Posted by epoxyman

Hi Doug
You are right I had a senior moment - ratio is 2.36:1

the maxprop is 17 in 16 deg pitch right hand rotation

The fixed prop that I am looking at is 18 in diam. 22 pitch right hand

The major issue with the classic 2 blade feathering prop may be that in most cases you need to hacksaw off the end of the shaft which would be the last threads and the cotter pin hole. I have not verified this with my shaft (need to disassemble the prop) but the videos I have seen on youtube and the manual for the 2 blade classic all show this. This basically will screw me for all replacement props - I have an email into DYI to see if their 3 blade classic will interchange. Otherwise I will have to replace the shaft too.-- NOT an easy job

You dont have to saw it off. At least I never did. That may be for using their special zinc maybe? not sure. I just zinc the shaft anyway. I really doubt the prop or being two blade is your issue. I have swapped 3 and 2 blade fixed props with little apparent change between them.

[NakedCity]

You do know that the pitch is adjustable on your Max Prop. Before I bought anything I would increase the pitch on your prop by at least 2 degrees or maybe more. 2 degrees should reduce your RPM by about 15% for the same speed. So 6 Kts @ 2400 rpm

[epoxyman]

That is the question I have.
If based on what the manual said and what I have seen on line - if when I open the MaxProp Classic and find that the shaft has been cut, then what I would want to do is change the pitch - if it is at 16 now would I want to change to 18 or 20??
I have watched the PYI youtube videos regarding taking the prop and gears apart and identifying the three gear settings (do 1 and 2 and the hub).

Since it is expensive to haul out - I was thinking along the same lines of increasing the pitch - PYI said "Anytime on a displacement vessel when a propeller gets close to square (Same pitch and diameter) the propeller becomes less efficient, and starts to spill water as it can not process it efficiently".
So why do they recommend 17in and 16 pitch for my application.
Doesn't make sense but I do not know what to try that would be a reasonable pitch change - the engine is certainly powerful enough and at 3000 rpm (max rating for engine) no black smoke - just not the speed one would expect

[Jim Cate]

No expert, but trying to put 55 hp through a 17 inch diam two blade prop seems pretty ambitious to me... no matter what the pitch. Just not much blade area here.

And question: are we sometimes confusing degrees of pitch and inches of pitch (strange dimension combination) here? Most props are rated in inches, not degrees. Supposed to indicate how far the prop would advance through a non-slipping medium in one full rotation.

Jim

[epoxyman]

Do not disagree with the pitch angle in degrees Vs. rotation of prop blade. Here is the explanation chart from MaxProp.
Still the question remains of the effect of blade angle on the speed and will it improve or is capable of improving the performance of my classic 2 blade.

Also this issue of requirement of cutting the end of the shaft.
MaxProp indicates that metric shafts do not require cutting only SAE.

[DougR]

I have taken a look at the numbers, and here is what they say for the parameters of your Cal 39:

Two Blade prop:
The most efficient two blade prop would be a 22" X 12" , producing the highest thrust @ 7.5 Kts and the most efficiency, and requiring a blade area ratio of about 38%. (This means that the area of the blades would need to be at least 38% of the area of a 22" circle).

Moving down in diameter it's 21" X 13" pitch, 20" X 13.5" pitch, 19" X 14.4" pitch, and as the diameter gets smaller, the blade area ratio goes up to maintain adequate surface area. The program chokes below 19" diameter because the blade area cannot be large enough to avoid cavitation and thrust breakdown.

To answer your questions as to why PYI recommends a 17x 16, it's because that combination of diameter and pitch will allow the engine to achieve its recommended 3000 RPM, not because it's the optimum propeller. Remember, you could tie a 2 X 4 plank to the shaft and restrict the RPM to 3000, but there wouldn't be any thrust. Also, the comment that PYI made about pitch/diameter ratio is correct. At the displacement speeds that we are discussing the most efficient props have a pitch/diameter ratio of about .55 or .60 . When you get into planning hulls the p/d ratios will approach 1.0 or more, and at more extreme speeds can go totally opposite into 2.0 or higher.


Moving on to a 3 blade prop-
The most efficient three blade prop will be around a 21" X 12" X 3, and moving down in diameter to 20 X 13, 19 X 14, or 18" X 15" X 3.

This means that the three blade fixed prop that you have is totally unsuitable for your use. You would have to repitch the prop from 18 x 22 down to 18 X 15, and that's basically impossible. Twisting a prop more than 2 or 3 inches of pitch can't be done without destroying the blades.

So......I would suggest looking around for a fixed three blade prop in the 18 X 15 range or maybe 19 X 14, and give that a try.

The Cal 39 MK2 can easily handle an 18" prop and even squeeze in a 19" prop with perhaps just a bit of tip noise.

From my personal experience with my own Cal39, I use an 18 X 13 X 3 folding prop with a 55hp engine rated @ 3000RPM and can turn this prop 2900 RPM and about 7.8 Kts. However, I have a 2:1 reduction transmission. Because you have a 2.36:1 ratio you will need about 2" more pitch to hold the RPM down to 3000.

DougR

[fstbttms]

Originally Posted by epoxyman

The major issue with the classic 2 blade feathering prop may be that in most cases you need to hacksaw off the end of the shaft which would be the last threads and the cotter pin hole. I have not verified this with my shaft (need to disassemble the prop) but the videos I have seen on youtube and the manual for the 2 blade classic all show this.

As previously mentioned, if you have an SAE shaft (and you do), the end of the shaft was trimmed off when your 2-blade Classic was installed. This the case with both the 2-blade and 3-blade Classic models. Metric shafts do not require modification.

Originally Posted by epoxyman

I have an email into DYI to see if their 3 blade classic will interchange.

There is no reason why a 3-blade Classic can't be installed on your boat. Further, there is no need to haul the boat to do this.

[epoxyman]

DougR and all thank you,

DougR - question regarding the pitch in inches Vs. setting angle. The numbers you quoted for the prop on the Cal 39 - were you quoting setting angle or pitch in inches. The reason I ask is - since the quotes from PYI are:

2 Blade Classic 17” diameter by 16” pitch for a 1 1/4" shaft $2000.00
3 Blade Classic 17” diameter by 14” pitch for a 1 1/4" shaft $3350.00
3 Blade Easy 17” diameter by 14” pitch for a 1 1/4" shaft $3350.00
4 Blade Easy 17" diameter by 13" pitch for a 1 1/4" shaft $3750.00

I am correlating the existing prop I have (17x16x 1.25) If I go by the chart that I put on my last post this would mean that the setting angle is 26 degrees for a 16 inch pitch in inches. This would seem excessive based on how the prop looks when rotated (pictures attached).

So my questions are:
1) could my existing prop installed by PO be installed with the wrong pitch angle or degrees, and therefore explaining some of the inefficiencies?
2) From the quote above is he inferring pitch angle in inches or should this be degrees - for settings on the hub

I sent PYI yesterday the question regarding if a 3 blade classic can use the same shaft assembly. It would seem that if I don't want to replace my shaft - I must go with a replacement MaxProp - I do not believe that it now would work with a FlexoFold which is about $1,000 cheaper and is folding - better for Maine

Again - thanks gentlemen

[DougR]

To answer your question:
- All of the info I provided relates to pitch and diameter as stated in inches

I can't answer your other questions as to the current prop or what others are referring to.....

From the pictures and dimensions provided, it's evident that you are not restricted to a 17" prop diameter, so go with a larger diameter, because you are suffering from lack of blade area. You can easily fit an 18" in the available space and still maintain 15% tip clearance, and you can get a 19" in there with 10% clearance.

DougR

[epoxyman]

So DougR

On my 17x16 If I read the MaxProp chart correctly (attached in prior post) for a 17 inch diameter if I wanted a 16 inch pitch I would go to the settings for a 26 degree setting angle, and if however the PO had used a 16 degree setting angle (mis-understanding the terminology) he would have set a 9.1 inch pitch.
Clearly this type of mistake must happen regularly - If this is the case then the prop would have a very poor angle of attach to the water and would result in significant reduction in push. One thing I was noting was that from the start (at initial engaging) I could hear what sounded like cavitation, and that it took some time and changing the throttle to reduce the noise. This may point to a possible mis-setting of the pitch.
Does this make reasonable sense??
Again thank you

[fstbttms]

Originally Posted by epoxyman

...could my existing prop installed by PO be installed with the wrong pitch angle or degrees, and therefore explaining some of the inefficiencies?

Of course it is possible that the prop is pitched incorrectly.

Originally Posted by epoxyman

I sent PYI yesterday the question regarding if a 3 blade classic can use the same shaft assembly.

I'm sure PYI will respond tomorrow but as a PYI-recommended installer, I can assure you that yes, a 3-blade Classic can be installed on your existing shaft.

I sent you a PM.