Jeanneau Fantasia (27ft) Yanmar, 1GM10, reason for poor motoring performance?

[Ammonite]

Just trying to help out a mate....

He has a lift keel Jeanneau Fantasia fitted with a Yanmar 1GM10 with 2.21 reduction gearbox and Radice K11 2 bladed 12" x 8" RH prop. The problem is that he's only getting 3 - 4 knots max at the start of the season (with clean prop) and much less later on in the year.

My suspicion was initially that the prop was too small and was thinking along the lines of a 14" x 8" 2 blade (this is what Yanmar suggest for this engine/gearbox although in this case it wouldn't fit) or 12" x 8" 3 blade, as he's new to sailing and is keen to have decent motoring performance even if it means sacrificing a little sailing speed. However, when I spoke to Sillette (Radice dealers) they said that given the blade area of the K11 Radice that this was the prop they would suggest.

The boats stats are here http://sailboatdata.com/viewrecord.asp?class_id=627

The engine appears to run sweetly both in and out of gear and the exhaust elbow has been changed. I don't know the exact revs it's making as he doesn't have a tacho and given the advice from Sillette I was going to suggest putting her back in the water and using a photo tacho (£10 off eBay) to measure the engine revs and prop shaft speed.

If these aren't hitting the expected values then it has to be the engine / gearbox that is a fault but if the problem does turn out to be the prop he's going to be hit with the cost of another haul out.

What to do? I still can't helping think that the 12" x 8" Radice is too small but given the cost implications I don't want to give him the wrong advice.

Thanks in advance

 

[FWB]

14x8 for 2 bladed prop.
See here...
http://www.marinedieseldirect.com/yanmar/shopping/parts_references/prop.php
Scroll down

 

[Seajet]

Chaktoura,

it should be a relatively easily driven hull, does the engine shoot straight up to high rev's, ( going by ear ) an indication of being underpropped ?

How about the temperature ?

3-4 knots sounds way too low.

I'm not familiar with the Radice prop, but if it's a folder, is it unfolding correctly ?

 

[Ammonite]

Chaktoura,

it should be a relatively easily driven hull, does the engine shoot straight up to high rev's, ( going by ear ) an indication of being underpropped ?

How about the temperature ?

3-4 knots sounds way too low.

I'm not familiar with the Radice prop, but if it's a folder, is it unfolding correctly ?

It sounds like it's achieving 3000+ rpm to my engineers ear Will check this out with the photo tacho when it's back in the water. I was wondering if the clutch was slipping (if the prop turns out to be correctly sized) as there was almost no wash coming out of the back when in gear alongside the dock (but surely the gearbox oil would be black with friction material if that's the case and it's completely clear?). The K11 Radice is a turbine style fixed pitch prop i.e it has more blade area than a regular sailing prop.

foeu - yes, that was the site I came across too.