Boat overpropped - need help please.

Ok, I trust your rpm readings. If you are not aiming at top speed, you will get slightly lower fuel consumption with some "overpropping". In this case you will find a reasonable compromise with a diameter of ~19,5"; ie 495 mm. Max engine rpms will be ~2680 rpm.

 

Thanks Baeckmo,

So I should go with a reduction in diameter from 22 to 19.5" and stay with the 17" pitch?

If they decide that the pitch can be modified should I go with 21x15" as given by propcalc?

Thanks,

Daniel

 

Yes, and yes (and your'e welcome).

 

Hi Baeckmo,

Thanks for the advice and I will keep you posted about rhe results.

Meanwhile I have another problem... Just last night one of my employees called me to let me know that another tour boat of mine just lost a propeller during a morning manouvre. I'm not sure we will be able to recover it as the water is 6-7 m deep and the current very strong.

I'm not sure what the characteristics of the propeller where as it had nothing written on it. I'm reluctant to buy a new prop as I might repower next year so I've been looking on eBay to find a matching one.

The boat is:

Length - 8m
Beam at water line- 2.8m
Draft without keel - 1m
Engine - 45hp@2400rpm diesel
1:2 gearbox
Two bearings on schaft

Propcalc is recommending a 19.1x12.3 3 blade prop and a 18x12" four blade prop.

https://www.ebay.co.uk/itm/331856818129
https://www.ebay.co.uk/itm/222108668647
https://www.ebay.co.uk/itm/231928372552
https://www.ebay.de/itm/201586495210

What do you think?

 

When in gear it will not exceed the 2000rpm mark. And you can feel the engine is struggling.

Your boat may not be "overpropped" it might be setup forv economical cruising.

A boat that plaines will require max RPM, usually to get out of the hole.

A displacement boat will only go so fast thru the water, before the power requirements get crazy.

An 8 meter boat will run about 6K,,, 6 nautical miles per hour.

How heavy is your boat?

And with 45 HP do you really expect it to plane?

What speed do you get at 1700 or 1800 RPM now?

 

Hi Fred,

Sorry for the confusion, but this is a second boat I'm talking about. Please read the last post. The fist boat is overpropped the second just lost it's prop and I'm looking for a new one.

2000 max rpm with the first boat it's seriously overpropped and I don't think it will be optimum for consumption. I have cleared that out with Baeckamo.

The boat will actually semi-plane due to the added appendix. See pictures.


I'm going to move the last one in a new thread.


Cheers,

Daniel

 

Hi Beckamo,

I found this four blade prop - what do you think about it? Could it work?

18x15 RH - 4 blades
https://www.ebay.co.uk/itm/231928372552