Boat Builder Central - Builder Forums

Looks good. Nice work!

Peter
LUS

I'm posting the question also here:
Finally, I'm going to buy a propeller now for the TW28. But... there's no exact answer and I'm a little bit confused.
I have a Beta Marine 43hp (Kubota) 2800rpm engine with TMC60 (2.54) and a Python Drive in front of the 35mm axle. Now, Jacques proposed a long time ago a 17"x13" propeller for a similar engine and transmission, but the dealer suggests to me 19"x17". I wanted a 19" 3-blade propeller as there's enough room.
I checked different online pitch calculators and I'm even more puzzled. The data ranged from 19"x11" to 19"x14" and one calculated the same 19"x17" dimensions as the dealer offered. So, maybe this last dimension could work.
But I would like also to ask for real experiences from builders and practical people as obviously there's no hard science working here. Especially because the hull of TW28 with box keel is not common.
Wish you nice summer on your boats or successful boat building.
Dario

Does the prop supplier offer a re-pitching service for a fee? If so, suggest you go with the largest practical diameter, and a somewhat conservative pitch. Use it for a season, gather data, and then re-pitch if required.

glossieblack wrote: ↑Thu Jun 23, 2022 6:48 am go with the largest practical diameter, and a somewhat conservative pitch. Use it for a season, gather data, and then re-pitch if required.

That sounds clever, thnx

glossieblack wrote: ↑Thu Jun 23, 2022 6:48 am Does the prop supplier offer a re-pitching service for a fee? If so, suggest you go with the largest practical diameter, and a somewhat conservative pitch. Use it for a season, gather data, and then re-pitch if required.

Glossie is spot on. You do not want to over prop the engine as that is a good way to kill it. Fully loaded boat with all the weight it will ever carry and the engine should still reach full rated RPM. You do need to be a little close on the prop as there is a limit to how far a prop can be re-pitched. For a 19-20 inch prop you need about 3 inch clearance. I would go with the biggest dia prop I could swing.

Dario,

I have a very similar setup: 42 HP Mitsubishi, TMC60 with 1:2.5 reduction, Python drive and 35 mm axle.
The propeller is 19x13. Cruising speed is app 10 km/h at 1700 rpm. At 800-900 rpm speed is 6 km/h. For manoeuvring a lower speed would be easier, so perhaps the pitch is a little high. On the other hand the 1700 rpm is a good compromise with regard to noise, so I am not really considering changing anything. With this setup the Luka needs a little less than 1,5l/h which is quite nice considering current diesel prices.
I do not think the setup can handle a 19x17 prop, to me me the pitch is way too high.

Good luck, looking forward to a splash.
Regards,

Peter
Lus

Dario totally agree with Luka you do not want to over pitch this your motor.

Tom

Thanks for the excellent advice,
yes, I've also doubted the suggested pitch. I'm expecting cruising speed around 5kn and enough thrust for sudden gusts of bora, the strong wind falling from mountains toward the Adriatic sea.
Peter, I have just one question more... do you reach max rpm? (in my case 2800)
I wish I could drink a beer with you

TheBroomside wrote: ↑Thu Jun 23, 2022 3:00 pm Dario,

I have a very similar setup: 42 HP Mitsubishi, TMC60 with 1:2.5 reduction, Python drive and 35 mm axle.
The propeller is 19x13. Cruising speed is app 10 km/h at 1700 rpm. At 800-900 rpm speed is 6 km/h. For manoeuvring a lower speed would be easier, so perhaps the pitch is a little high. On the other hand the 1700 rpm is a good compromise with regard to noise, so I am not really considering changing anything. With this setup the Luka needs a little less than 1,5l/h which is quite nice considering current diesel prices.
I do not think the setup can handle a 19x17 prop, to me me the pitch is way too high.

Good luck, looking forward to a splash.
Regards,

Peter
Lus

Dario,
I have the same engine as Peter, only mine have a 30mm axle. My prop is 16x14 . The cuisine speed is 10 km/h at 1600 rpm and uses 1.6l/h. So my conclusion is: no difference. But my feeding says that a 19 inch prop can transfer the power beter in the water. Max rpm +/- 2500 2600 with a lot of norse and a speed of +/- 14km/h.

Allard.

Thank you, Allard!
I needed your advice. Now I'm more confident.
I hope I'll get a good price, some producers want from me over 1000eur...
regards
Dario