I am considering Beta for repowering my full displacemet (canoe stern) trawler 36'LOA, 33'LWL 23000lbs. Currently it has 50SHP continous @ 2000rpm diesel w/ 2.6:1 BW & 23 X 20 LH 5 blade (narrow blade "shrimper") prop. She cruises 5.8K @ 1200rpm or 6.3K @ 1300rpm (top speed @ 2000rpm = 8K) The prop.HP curve on my engine's chart shows that I am using 10 and 13HP at my two cruise speeds and 48HP at top speed (which I almost never use) I am happy with all aspects of this installation and performance but there are no parts available for this engine to speak of any more and it has countless hours on it. Which Beta engine do you recommend for me? Can I use my existing BW transmission if I repitch (max. 2") my prop? Can I retain my existing prop if I go to 3:1 ratio? Thanks in advance for your response/s. John
Your boat sounds very interesting. You have 2 choices of engine to do what you want and give you similar performance. We often supply engines with our Velvet Drive adaptor kit. This includes the 2 stage drive plate, adaptor plate, correctly sized oil cooler, hoses, studs etc.
1) The Beta 60 develops an honest 58.5HP at 2,800. If you use this engine with a 3:1 transmission you will want to re-pitch your propeller to 23"x18". You will still get 8Knots.
2) If you go up in size to the Beta 75, you can keep the 2.6:1 and with the same prop change (to 23"x18") you should max out at 8.7Knots.
Both of these engines are naturally aspirated and slow turning by todays standards and both are happy to run at low speed all day without any issues.
Stanley, thank you very much for your prompt consideration of my repowering situation. Your answer raises several questions for me however. 1) Why would I need to use 58 or 75 HP to do what I am now doing with 50HP (and do very seldom at that) 2) If I am correct in my belief that I am only using 11-14 HP at cruise would not the suggested engines be very underloaded to their possible detriment. I had tenatively planned to use less horsepower than I currently have thinking that my hull speed is only 7.5K anyway and that I would only need intermittant power at that loading also. I also thought that cruising closer to maximim rated HP would increase my efficency too. Maybe I am talking about a "different kind" of horsepower being generated by my current engine using 277 ci displacement to develop 50 SHP @ only 2000, and that is what I am not taking into consideration. John
Wow, 277 cu-in. That is a monster. The Beta 60 is only 148 cu-in. Your paramaters are 50HP at 2,000RPM and you want to keep your current 5 blade propeller. The Beta 60 will give you 47HP at 2,000 so I had to work back from that.
Torque plays a bigger part in moving a displacement hull than horse power and your old engine has plenty of torque. If you want to use an engine with less HP, you will have to change your transmission and propeller. The smallest engine that I would recommend is the Beta 43. The newest versions of this engine are 122 cu-in and this engine develops 43.7 HP at 2,800 RPM. If you use a 2.57:1 transmission and a 21"x14" three blade propeller you should achieve 7.6 Knots if you run flat out.
The whole idea is to have a quiet, economical and stress free cruise with enough reserve power for when you have to rush or for when the weather turns nasty.
I hope that this helps to clear thing up a bit. Regards, Stanley
Stanley, Thanks again for trying to clear up my questions. Let me see if I understand... Running the Beta 60 at 2000 rpm would give me aprox the same HP/RPM as I have now so I could then use the same reduction ratio and propeller that I have now (give or take 2" pitch) Right? How would the engine be limited to this rpm so it would not overload? Not just by the propeller, I would guess, because the engine would be way overpropped if I applied more power after reaching 2000 rpm. So I would assume the full load stop would have to be adjusted to the minimum which would let me reach 2000 RPM (at which point the engine would be producing 47HP) and no more. I always wanted to use a larger engine at a lower rpm to produce my power, all things being equal, more like an 1800 rpm generator set; by running the propeller load curve up to the full load curve at 2000 RPM (47HP) rather than at 3000 rpm (58.5HP) I have suspected this might be done but others say "it will overload" and " these new engines are not meant to be run like that", "it will glaze up", "it will carbon up" and so on. So, is there any downside (to the engine and its warranty) to doing this? And how would the power be limited? John
When we work out a propeller calculation, this will generally allow the engine to reach its rated maximum RPM (2,800 in the case of the 60) in gear plus / minus 100 RPM. This will allow you to have a good cruise and maximum speed. If the figures that you have provided are correct, the engine will not be forced to run in an overloaded (or overpropped) condition. As these engines are happy to run at any speed above idle all day, you need not worry about glazing up cylinder walls or carboning up. Many of the Beta Marine diesel engines are used on the canal boats (narrow boats) in the UK where there is a speed limit of 4MPH!. These engines run at low speed all day and work well year after year.
As I said in my first reply to you, The Beta 60 develops an honest 58.5HP at 2,800. If you use this engine with a 3:1 transmission you will want to re-pitch your propeller to 23"x18". You will still get 8Knots. With this combination, you will achieve what you want.
Stanley, I think I've got it now. You are selecting prop and transmission for 58.5HP @ 2800 and saying run her at 2000 (48HP). But I don't run at that speed, I only run at S/L 1 or 1.1, 5.75-6.25K, which requires only 10-14HP and that would, I thought, underload any 60HP engine.
That brings me back to what I thought you were suggesting: Using the 60 or 75 engine but extracting only 50 HP max. not by limiting it by the prop load but by adjusting it on the governor so as not to overload it after reaching 2000 rpm. This must be how the generator sets are done, and maybe the canal boat models, govern AND prop to whatever HP is available at 1800 rpm and no more.
Dont worry. You can run this engine at any speed from idle to 2800 without problem. If you want to cruise at 1200 or 1600 RPM that is ok.
When you adjust your throttle control, you are controlling the governor. These new Beta Marine engines are not like the diesel engines of 50 years ago. If you contact me at the office during normal working hours and let me know where you are, I may be able to arrange for you to see someone else's engine and how it runs.
