Victoria Shadow Association Members' Forum

Simon_Fayers

Member

Registered: 2002-07-05

Posts: 12

cutlass bearing and prop size.

I replaced the 1GM on my Frances 26, Shebeca last winter with a Beta 16, having previously had a Beta 13 on my last Frances. In terms of fitting into the available space and price wise, it was the best engine option and I am very pleased with the installation.. Lots of conflicting advice on prop sizing, the prop for the 1GM was a two bladed 12x11 and I wanted to stick with a two bladed for better efficiency when sailing. Advice for the 16hp ranged from sticking with the 12x11 , this apparently being the correct size for the 16, (the same supplier later suggested a 14x9!), up to a 16x10 which clearly would not physically fit and even my 5 year old granddaughter could see it was a little large. 3 bladed no problem, most suppliers agree on either a 13x9 or a 13x8. In the end I opted to repitch my existing prop to 12x11.5 and see how that performed. Only later in the season with the hull well weeded up did it seem to struggle. Over 2000rpm I would get a rumbling noise from the stern locker. I tried adding insulation, no difference. I assumed that the prop was slipping/cavitating under load as it could not push the upside down forest through the water efficiently. However, having reread some articles in the technical manual ( waterlines spring 1993 issue 4), I see that if the cutless bearing protrudes or has not been cut in half then that could cause rumbling?, I am not sure why it would, but I did ask for a half length to be installed. It currently sticks out from the housing by about 12mm. Should it be flush with the housing, I honestly cant remember? Could this cause the rumbling, (It wasnt at the start of the season and Shebeca easily reached 6 knots with the modified prop). I am leaning towards her being under propped and have purchased a second hand 14x12 to try next year. (I may have to grind it down a bit if it struggles to reach max rpm). Its all a bit of a trial and error black art. I wanted to avoid a feathering prop due to cost and maintenance and also a fixed two bladed prop in my opinion, lines up nicely with the dead wood when locked in gear. Any advice welcome. Simon.

Simon_Dewing

Member

From: Torquay / Texas

Registered: 2022-08-04

Posts: 63

Re: cutlass bearing and prop size.

Simon,

Cutlass bearing should be flush, sounds like it wasn't cut.
Mithril's arrangement with 3 blade prop

line cutter wouldn't fit without it being shortened.

Likewise I have an annoying vibration at higher revs which I put down to the amount of growth (mostly sea squirts) that the prop seems to attract.

Always possible they fitted a 1 inch bearing on a 25mm shaft (I have a leak whilst running from the Volvo shaft seal and I believe this to be the cause). Have to get her ashore and swap it out but not yet had time.

Simon

Simon_Fayers

Member

Registered: 2002-07-05

Posts: 12

Re: cutlass bearing and prop size.

Hi Simon, thanks for your reply. I offered up the 14 inch prop today as well, slightly too large. With the cutlass bearing cut flush and a bit of length taken off the shaft, should be fine. Cutlass is 25mm on 25mm shaft. Hardy chaps those little sea squirts.

Jonathan_Hopper

Member

Registered: 2004-03-23

Posts: 161

Re: cutlass bearing and prop size.

Cutless should be flush with the holder, though I am surprised a small overhang might cause any problems (so long as any rope cutter has clearance, and there is sufficient shaft to cope with engine movement under power).   Francesca had a new cutless this season, and was left overhanging by a few mm to help removal next time, with no significant noise that I have noticed - perhaps half the overhang you describe.

End of season fouling etc. can do funny things to speed, noise, cavitation etc. and may well be the source of your noise.   When I took the shaft out over the winter it was covered in scale from the cutless back to the stern gland, and wonder if this could also be a source of roughness at times.   Given it is a noise which has come on during the season then fouling seems high on the risk list, or perhaps something like some fishing twine wrapped around the shaft.

In the past, on a drying mooring, a new cutless always gave a grinding noise when first getting underway, until the cutless had worn a little.

Do you know good the alignment is?   Perhaps a new cutless might be more sensitive to small misalignment.

6kn from a 2 blade prop on a Frances sounds impressive to me.    I have played with several 3 blade props with a Beta 14, and think that all have their qualities and downsides.    Could you get to full rpm using your 12 x 11.5?    If so, then you could go for something more powerful - achieving more like 3400 is acceptable and will tell you when your prop is in the right sort of area as regards size.    Suspect something like a 13 x 11 might be worth trying, but Beta ought to be able to recommend a good starting point https://betamarine.co.uk/seagoing-propellers/ even if you choose to 'tweek' it a bit depending on your priorities.   Off course it may be possible that you cannot put a powerful enough 2 blade prop on to soak up the 16hp (there is only so much pitch you will want to use), but no idea if you will reach that limit.

Do you paint your prop?   Something like Silic One or Velox are well worth applying in my experience.

Regarding noise, cavitation doesn't really give you a rumble.    Presume the cutless hasn't come loose in the holder and is rotating - don't see why it should.

Would be interested in hearing more about your Beta 14 v's 16 experience.   Not may will have been able to try both out on the same boat!

Simon_Fayers

Member

Registered: 2002-07-05

Posts: 12

Re: cutlass bearing and prop size.

Hi Jonathan, thanks for your suggestions and comments. The alignment is good, I installed with the help of a professional. We put the beta on alloy beds to achieve the correct height and alignment. All looks well there and the cutless is new. It is also attached and not turning with the prop shaft. Regarding prop size, I had a 13x11 two bladed with my beta 13.5 and that worked well which is why I have opted to try a 14x12 (second hand). It is slightly too large for the aperture but if the cutless is cut back and 20mm taken off the shaft at the far end then it would fit. Not sure what a safe gap between rudder and prop should be? Not less than 1cm I should guess incase of debri jamming in the gap. In terms of pitch, as far as I understand it a bigger pitch will give better cruising rpm at the expense of acceleration. As any long keeler is not good at close quarters manoeuvrability, my priority is to get maximum fuel economy at a decent speed when making passage whilst also providing sufficient bite when motorsailng against the wind and sea state. In a marina manoeuvre making best use of any wind and tide and warps rather than prop power. Having skippered several fin keelers in the past, they are such a joy to drive around marinas!. Again with prop sizing being a black art it may be that on a craft as small as the 26, the difference in drag from a 3 blade to a two blade is maybe academic but one has to try!. Regarding painting the prop, I have in the past used prop grease but last season used hempel spray on prop gaurd. Both with varying results. This season just gone in the Helford was very weedy for everybody I have spoken to. In terms of difference between the 13.5 and the 16, no real difference as yet, its just that I was fitting a new engine and the 16 fits fine. With the right prop next season I will let you know if there is any noticable difference if I mess up with channel Island tides!.