Prop Info

[Garygee]

I am now the proud owner of a Ribcraft 7.8 and have been playing in and around Milford Haven for the last week.

Chickened out bringing it home though with a new boat, low engine hours and Force 7's at sea.

I have now a few hours on the engine/leg, (12 hours) and think it might be under propped.

It will rev round to 3600, 300rpm (on the built in tacho) over the max with no lag or build up what so ever. Speed is a little under 40Kts

The prop/s are a 22" stainless cupped prop, on a Bravo 3 leg, cant find a diameter stated on the prop.

So a few questions does this sound under propped?.
What effect does the "cupped" on the prop make.
What does other people use on the Yanmar 240/Bravo 3

Boat is not light but only usually carrys four people and 60 gallons of fuel.

What do people think

Regards Gary

[Garygee]

After some digging on part number the diameter is 15.75"

Regards Gary

[Simon Guest]

Hi Gary,

Bet you're pleased finally to have your new boat!

Did you talk to Ribcraft about this? They used to do a free prop exchange if you thought you had the wrong prop - do they still?

Do tell us how your new 7.8 compares with your old 4.8.

cheers,
Simon

[Cookee]

Gary

Cupping on a prop gives more lift to the front of the boat, the same effect as trimming it out, but using the shape of the prop to do it instead. It's more efficient but when you are heading upwind in heavier conditions it makes the boat want to fly, but faster in flatter conditions!

This of course only works if your boat needs more lift to the bow!

[Garygee]

Thanks everyone,

Have arranged a prop swap with Ribcraft, they recomended that we go from the 22 cupped to the 24 stright.

Should have them next week but it will be another week before we can try.

As far as being nose heavy, not sure, but with most diesels she is very stern heavy.

This may explaine why i could run with the leg almost fully trimmed in and still be running quite level.

Also if cupping the prop makes them more efficient, will i gain any extra speed going from a 22 cupped to a 24 stright ?.

Thanks Gary

[Mike Garside]

Gary, having just been through the new Yanmar engine and Bravo leg thing myself I can, without hesitation, recommend you get in touch with Joe Poulter. He is the travelling Yanmar expert and part of the new delivery deal is that he will come and spend time with you and your new boat to see that the whole combo is performing at peak.

Both Brian Elliott and I have each had a half day with Joe and are delighted with what we found out in the process. Let me know if you want to know how to contact him.

[Garygee]

Thanks Mike

Yes details would be nice, even if he does not come out is worth having a contact to pick his brains.

Regards Gary

[Mike Garside]

Gary, I have sent you a pm....