Propeller rotation

[Andrew Hollway]

I have just fitted a new Brunton autoprop on my 331 Senitoa. It turns out that the rotation of the new prop is wrong handed, it is a right hand prop but should have been left hand. I have sorted it out with Brunton’s who are going to supply a replacement and I have nothing but praise for the way they have dealt with it. It made for a very interesting launch!
The error has raised an interesting question about the sources of information on propeller rotation which I have not been able to solve. My engine is a Yanmar 4JH3-TBE with a Yanmar KM4A gear box. My owners manual specifies the propeller rotation is left, viewed from stern, ie anti clockwise rotation. All other information that I have found indicates the propeller should be right hand, ie clockwise viewed from stern. The Yanmar manual for the 4JH3 engine downloaded from the internet gives the various gear box alternatives, including the KM4A, and they all indicate propeller rotation clockwise viewed from stern ie right hand. The owners manual, downloaded from the internet also shows the propeller to be right hand but the engine being 4JH4-TE. I do understand that Nauticat changed the engine to the 4JH4 sometime in the mid 2000’s. Although I specified a left hand propeller, this conflicting information does account for the confusion.
The problem is in the process of being solved with Brunton’s supplying a replacement propeller, this time Left hand. I am, however puzzled why Senitao seems to be alone with a left hand propeller. Can anyone explain when Nauticat changed the rotation direction of the propeller on the 331 model and why the Yanmar manuals indicate a RH propeller when they clearly produced some engines for LH rotation?
Thanks in anticipation.
Andrew Hollway

[Robin Shaw]

Andrew I have a 331 which was fitted originally with a fixed lh prop. I have fitted a Bruntons Autoprop and took the opportunity to specify mine to be right hand. I did this because my regular berth is port side to and it is very handy when going in bows first as the powerful prop wash kicks the stern in nicely. As far as the engine and gearbox is concerned you can have either lh or rh it makes no difference as they are the same ratio, if you do change you obviously also have to swap the cables to the morse controls. I do find the Autoprop matches boat very well but you have to stay alert to what it is doing. Robin Shaw (Ambassador)

[Andrew Hollway]

Robin. Thanks for your reply. When the problem ocurred, I consulted several Yanmar dealers who all said the gear box would be damaged by swapping the morse controls on the basis that the gears are designed to resist the forward thrust in ahead and vice versa in astern. Yanmar website also said that the propeller direction for the gear box was RH. It was on that basis that we felt the only sensible solution was to replace the propeller. I’ve since discovered that the gear box is actuallu bi-directional so we could have just changed the controls. You don’t find that information on the various websites.
By the way, we have met before. You very kindly took us out for a trial sail in the Solent 2 years ago, arranged by Clive Stratton. You were, at the time, considering selling your boat but clearly that has not yet happened. We found Senitoa in Scotland in late 2018 and kept her on the Clyde until last autumn when we brought her to Holyhead, planning to move to the South coast this spring. Covid put paid to that so it’ll probably happen next year. Regards, Andrew

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