Last year I repowered my 26C with a Beta 20. I am very happy with the engine. My concern is speed under power. This has been an unusual season on Lake Ontario and I have done more motoring than usual when cruising. Normally I avoid motoring and will sail at 3 kn if it’s not a long passage.
With the original Varifold prop (for sale) Tiroc reached 5 kn at 1750 rpm and 7 knots at full power, 3150 rpm with the Beta 20. My mechanic told me I needed a different prop to allow the engine to reach, or almost reach a higher max rpm (3600)
With a two blade custom ordered Varifold Tiroc reaches about 3.7 kn at 2000 rpm, about 4.8 kn at 2400 rpm and 5.5 kn at 3450 max rpm.
As expected cruising speed changes with wind speed, direction and wave action.Recently we were making less than 4 kn at 2400 rpm into a 10 kn headwind (typical) and light chop.
There is a thin film of growth on the prop which I understand can lead to loss of efficiency and speed.
I could presumably increase the boat speed by adjusting the prop to greater pitch, but I’ve been told not to reduce the max engine speed which I would expect would be the result.
I’m curious about the experiences of others with a varifold prop and what type of prop other Beta owners use and their thoughts on speed under power. All helpful thoughts and opinions are welcome.
With our 26 and the Beta 20, I try to maintain a cruising speed of 6 knots (GPS indicator) so the engine speed does vary a bit. No wind, about 2600-2700 rpm will push her at 6 knots, with wind and waves, the engine speed will go up a bit. Max engine speed is 3600 (according to the specs) so 2700 is 75% loading.
Above 6 knots, the bow goes up, the swim platform is under water, and the fuel consumption goes through the roof, so 6.x knots is my typical cruising speed.
The prop is, from what I can see, the original Michigan 3 blade that came with the boat with the W13. I keep thinking of changing it to a Campbell Sailor, or a folding/feathering, but, as you say, with the winds on the lake this year, more motoring and less sailing has been the hallmark of this season!
Nice to hear from you; Cat’s Whiskers crew says a big “Hi”!
Couple of things to remember. A diesel engine should be run at 80% of rated rpm. Set it there all day long. They like it and need it. Slower is not good for the engine over the long run. So constantly running at say 1700 rpm is not a good thing to do. The prop and engine need to be matched to obtain this performance. Most prop manufacturers will do the calculation for you.
Properly matched you should be able to turn the engine at full rpm for a minute or two without any noticeable change in the exhaust emissions.
As for cruising speed. At 80% my Westerbeke 21 pushed by a 12x15 Gori two blade I get 5.2 in flat water. It burns .4g in the process.
If you are getting to say 5 knots at 1700 rpm something is out of spec.
I did find out something a few years ago. A 14x11 3 blade fixed prop was spec for the engine and it ran smother than the 2 blade 15x12 Gori and pushed it at 5k @ 80% ,. But in windy or high current the boat slowed by a knot. It’s not an exact science.
My 26 is powered by a Universal 16 which is a slower revving engine with maximum output at 2,800RPM. Mascouche is Hinterholler’s prototype 26 which he took to the North Channel for sailing trials. He must have been in a rush since he had to increase the size of the rudder to maintain control. He fitted a small 2 blade flex-o-fold designed for a gas engine since it was in stock. The engine never had enough work to do to bring it up to working temperature. When the engine was flat out speed peaked at 4 knots in dead air and calm water. The first thing I did was to order a three bladed slipstream s/s folding prop from Seahawk for the 2007 season. I was amazed that Ben Hawke was able to match the new prop to the 26 year old engine perfectly. I chose the Australian firm because the Canadian dollar had tanked and it made European props prohibitively expensive for me. Now I cruise at 4 knots comfortably at 1900 rpm with a maximum of 6 knots when the engine is running at 2,800 rpm.
To prevent “squatting” at speed, causing a moustache to form on the transom when the exhaust was buried, I fashioned copper cowls to fit over the cockpit drain through hulls.
These introduce air bubbles between the hull and water to stop water from clinging to the hull. This has proved to be an effective cure for sooting the transom. An additional benefit is that I achieve higher speeds at lower lower rpm which reduces fuel consumption and noise. This winter I intend to fit larger cowls to see if they produce greater speed at a given rpm. Regardless of the outcome they solved the moustache problem at minimum cost. Others have gone to great expense and labour reconfiguring the exhaust system.
Those of you with the more powerful Beta 20 may find that you can achieve 8 to 10 knots when cowls are fitted to eliminate the tendency for 26’s to squat when speed increases.
Rob, when I haul out on October 4th, I will take a close up photo of the cowls. In the meantime here is a photo of her transom after haul out in 2019. The cowls on the through hulls are just visible above the antifouling. Both Pondus and Mascouche lack moustaches. The cowls worked for me. An electric motor worked for Pondus and extends her sailing season without the worry of winterizing her.
John,
I am very interested to see what your cowls look like. Cleaning the diesel smudge is about the least fun ownership task on my Nonsuch. Thanks,
Greg Silver
Misty Cat 26C #121
St. Peter’s, Cape Breton
Mike,
What reduction gear do you have in the transmission?
The Beta dealer out here suggest we cruise at 2700 to 2800 rpm. That gets me 5.5 to 6 knots depending on conditions. It is a bit hard to say because I normally have the sail up and can get a bit of a boost even in very light air.
I have a 2:1 reduction gear. My brother has 2.4:1 (I think) in the trans on his Beta 20. I am current run a 3 blade Max prop. When the Beta first went in I used the 2 blade Max prop that was mated to the Westerbeke 13hp. When the hull was clean the 13w would push the boat to 6 knots at 3000 rpm. With the same pitch setting the Beta would reach 3600 rpm and about 6.5 knots. When I got the 3 blade PYI told me the setting would work out to the same as the 2 blade. With that setting the engine would only reach about 3100 rpm. I changed the setting and with a clean hull and flat water it will hit about 3400 so it is still slightly over propped.
If I run at 2500 rpm the water temp never goes above 165 degrees. If I run at 2800 it goes to about 175. I have to run ay 3000 or higher to get the temp up to 185 degrees and the thermostat starts to open.
Off the top of my head I can’t remember the prop dia. and pitch.
