Propeller specification for Beta 30 engine

[claude]

Dear HC33 Owners,

I'm staring plans to change my engine from Yanmar 3QM30 to a Beta Marine 30. With this engine, the propeller will revolve faster: transmission ratio would be about 2.5 instead of 3.0. I expect having to change the propeller.

I contacted one of the key propeller vendor, providing details of the HC33T and of the Beta 30, and received a suggestion to go for a 17" x 10" 3-blade propeller.

Has any of you changed his/her engine for a Beta 30? If so, I would appreciate details on gear-ratio, prop diameter and prop pitch used, and of resulting performance perceived.

Thanks in advance. Claude Labrie of HC33T "Slim Jack" based in Malaysia

[jonneely]

Hey Claude, I wrote a monster response to this with all kind of data but the internet died when I posted it and I lost it all. So I am going to paraphrase, sorry but I don't have the energy or time to do it over again.
Current 3qm30 @ 2600 with 2:1 make a max torque of: 166.63
To match the same shaft RPM and to keep the same prop which is ideal you can order the Beta 30 with a 3:1 gear box: 30hp@3600 w/ 3:1= 180.52 . If you go with the 2.1 stock box you will be running the prop much too fast and there will be a fair amount of cavitation. After speaking at length with two separate prop companies, Ideal shaft RPm for the HC33 is around 900-1000RPM, any faster and you will start getting squatting and cavitation. This is especially true with flat blade feathering props like our kiwi prop, even the current setup with the 3qm30 is too fast for it, requiring the pitch adjustment to be almost bottomed out.
Now for a little more money you can get the Beta 35 which produces 35hp@2800 with a 2.45:1 gearbox which will give you a prop speed under cruising conditions of about 930PRM with a max torque rating of: 221.14

Long story short for boats like ours, torque is king, its the power you need when you need it. The higher you gear up these engines the less efficient they are at delivering the horsepower to the shaft. With the necessary gearing the 30 needs it will be no more fuel efficient than the 35 because of the higher RPM, it will be louder and will require more maintenance over the long haul due to vibration and wear. Also the 4 cylinder will be smoother than the 3. If you look at the dimensions the 30 is not much smaller than the 35 either, so long story short, I would really recommend the 35. The same thing goes for the 38, which is the same block as the 35 but the 35 is detuned. Because of it higher RPM rating it actually has less torque than the 35. I am going to start ripping out my 3qm in 10 days, Ill post the process on SVprism.com


Cheers,

Jon

[andyv94]

Jon

What prop would you recommend for my boat, three blade prop.....not sure I want a
the type of prop you guys have.

Thanks as usual Jon

Andy

PS-the guys at Beta Marine recommended a 16x10 RH three blade prop, what do you think?

[jonneely]

So do you already have the beta 30? What gear ratio do you have with it? That will tell me what you should be looking at. Again you want the biggest diameter as possible, but if you have the 2:1 gearbox your torque curve is at 3100rpm so your shaft speed will be around 1500rpm so a 16 might be all you can swing.

[claude]

Thanks for the reply Jon. Sounds like you are proceeding with repowering to Beta 35. I'll be looking forward to read about the experience and outcome on your site, as suggested. In the mean time, have you confirmed that the Beta 35 can be accommodated without too much change to engine foundation? I read that engine has to be quite a bit lower than Yanmar to align with the propeller shaft.

There are quite a few posts of owners that have or were about to repower to Beta, so it would be great to hear about their selection outcomes and experience.

[andyv94]

Morning
I just bought a BM35 like literally minutes ago!! Very excited (wife, not so much ) it'll get to Puerto Rico in three weeks.
So now I weight to see how Jon does with his installation so that I can starts prepping for mine!!

So excited to not have to worry about parts, transmission, etc....it was a bit of a nightmare with the Yanmar
3Q30F

Cheers

[jonneely]

Beta 35 according to my preliminary measurements, it will need to be raised about an 1/2" to line up with the output tube. The reason is that the yanmar engine mounts are much taller than the betas. I'll know more once I get further into it. I'll keep you guys posted. I did order the beta with the shallow sump, the normal sump looked to be too deep for the oil catch to fit underneath.

[andyv94]

Question, what is the shaft diameter for the prop? Is it 1-1/4??

[jonneely]

Ours is 1 1/4" SAE threaded taper. I have been told that the 33 probably came with metric sized shafts originally so you need to measure to be sure.

Cheers,

Jon

[mimoza]

Still running the 3QM30FG on Mimoza
The shaft on Mimoza is 32mm with a metric taper (10:1) which is a little steeper than the standard SAE taper of 16:1
When we got a new wheel the prop shop had to fill and bore the hole since the stock one from Michigan Wheel was SAE.

[singlehanded]

Any advice or pics of the engine removal? I just bought a beta 35 at the annapolis show. My 3qm is running great, but parts and the Tranny made me lose faith.
Thanks Paul

[andyv94]

Jon would be the guy to ask since he installed his BM 35 himself

[jonneely]