10, 14 or 21hp?

JumbleDuck

JumbleDuck

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I am planning to replace my Yanmar 1GM10 this winter. I expect I'll go for a Nanni: the mounts are exactly the same width apart as those on the Yanmar and I don't fancy Beta, for several reasons. A first trawl through the Nanni range suggests that I could fit an N2.10 (479cc, 87kg, 10hp), and N2.14 (479cc, 92kg, 14hp) or perhaps an N3.21 (719cc, 106kg, 21hp) could be squeezed in.

14hp rather than 10hp for another 5kg seems like a no-brainer, but is it worth me investigating the three-cylinder option further, or would that be silly? The boat is 26' LOA, long keel, 4 tons in cruising trim and currently does 5kt under power in calm conditions. Was 23hp overkill for the Centaur?
 
One way to look at it is to compare what engines are fitted to recent boats of the same displacement. As an example a recent Bavaria 30 displaces about the same and has a Volvo D1-20. The modern trend is to fit more powerful engines than were generally used in the past. The 14hp engine would clearly power a Centaur, but the 3 cylinder engine might give you more thrust against a headwind or a chop, provided you could fit a big enough propeller, because the amount of power that you can transmit to the water is dependant on propeller blade area. I have seen Centaur's fitted with the Volvo 32hp MD11C, or a 20hp Beta BU722, so 21hp may not be excessive.
 
I believe many Centaurs were fitted with oversized Volvo's for commercial rather than technical reasons. I had a Yanmar 2GM on my Mirage28 which was plenty powerful enough at 16hp. I'd go for the 14hp twin cylinder which would be plenty powerful enough and much smoother than the single Yanmar.
 
14hp fine for that boat, and is a huge difference over the 1GM10. There are a couple with larger, but are a bit over the top. You also need to consider what prop you want to spin - a larger engine requires more rpm or a bigger prop, else you will not be able to transmit extra power. Diameter is restrictive - you can go to 13" but not much more.
 
If you had not already ruled out Beta, I think their 16hp engine at 599 cc twin cylinders would be just about right.
I have the Beta 722 (20hp) in a boat of the same type, 3 feet longer and maybe a little heavier. I have never in ten years time wished for more power and think that 16 hp probably would have been enough.
 
I would go for the largest engine if you can fit it in easily. On my boat(33') I was limited to a 13" diameter prop so was advised by various firms that 14hp was adequate, so decided on a 20hp but for a few pounds more they offered the 25hp. (Beta ) You will also get the advantage that as it is fresh water cooled you will be able to fit a calorifier and get HOT water!(keeps SWMBO happy) Check carefully that the existing exhaust system is adequate, change or upgrade it and fit a non drip prop shaft seal, possibly a new prop & shaft and new sound insulation.
 
I replaced my Jeanneau 25's 1GM10 with... Another 1GM10.

Fitted perfectly, took me (DIY) just over a day and at less then 100kg was a two person lift to get in.

No changes to engine beds, controls, wiring or any other stuff. Big improvement over a 25yo engine and I'd do the same again tomorrow.

Have you considered doing the same?
 
Nanni 14 will be fine. It is the same as the 10 except it has a bigger alternator and governor setting to allow it to rev to 3600. You don't have room to swing a prop to absorb the 21hp and that would be absolutely wasted. With a 12*9 3 blade prop you will get hull speed of just over 6 knots. Use the money saved to buy a Featherstream prop and you will have the optimum set up.

Yes, the 23hp was overkill in the Centaur, but that was what was available in the Volvo range at the time - the next size down was marginal, and it originally had a 13hp engine.
 
langstonelayabout said:
I replaced my Jeanneau 25's 1GM10 with... Another 1GM10.

Fitted perfectly, took me (DIY) just over a day and at less then 100kg was a two person lift to get in.

No changes to engine beds, controls, wiring or any other stuff. Big improvement over a 25yo engine and I'd do the same again tomorrow.

Have you considered doing the same?
Click to expand...

The Nanni he is thinking about is almost virtually a direct swap. Just marginally different mount spacing fore and aft, the exhaust is on the other side and is a different size. Not difficult to change the exhaust and the 2 cylinder fresh water cooled is vastly superior. Have actually done this in my own boat.
 
Thanks, folks, much appreciated. The boat isn't a Centaur, but close in size and weight. One big difference, which Tranona alludes to, is that the propeller is in a cut out between the stern post and the rudder - she's a double ender - so prop size would be one of the issues to investigate if I went to 21hp. I may well get a Featherstream, but I am a little cautious about having extra moving parts down there, so may just put up with the drag of my current (or a similar) three-bladed fixed prop.

A thought: should I be thinking about a Volvo Penta D1-20? 18hp and three-cylinder smoothness?
 
The Volvo is physically too big (I would think) and again you would need a 13 or 14" prop to absorb the power for no speed gain. Nothing to worry about with the moving parts of a feathering prop. Just a pump of grease and possibly change of anode once a year. You will find the difference from a fixed prop well worth it. That is what I have attached to my Nanni.
 
Tranona said:
The Volvo is physically too big (I would think) and again you would need a 13 or 14" prop to absorb the power for no speed gain. Nothing to worry about with the moving parts of a feathering prop. Just a pump of grease and possibly change of anode once a year. You will find the difference from a fixed prop well worth it. That is what I have attached to my Nanni.
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I have a 13" prop at the moment, but i don't think I could go to 14. I shall look at Volvo dimension - that third cylinder is seductive - but Nanni N2.14 is feeling like the way to go.
 
I'd agree with most of the advice so far. I installed a (Beta) 14HP into our 28ft longish keel boat. With a clean hull and 2 blade prop we will make 6.5 knots. I can't say that I have ever felt the need for more power.
I would also agree with the suggestion of a folding/feathering prop. I'd suggest flexo-fold, very simple and robust with very little to go wrong.
 
alahol2 said:
I'd agree with most of the advice so far. I installed a (Beta) 14HP into our 28ft longish keel boat. With a clean hull and 2 blade prop we will make 6.5 knots. I can't say that I have ever felt the need for more power.
I would also agree with the suggestion of a folding/feathering prop. I'd suggest flexo-fold, very simple and robust with very little to go wrong.
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Thanks. There is no room for a Flexofold in the cutout ... it really has to be a Featherstream.
 
Current Yanmar and Beta engines require larger diameter intake and exhaust than the older engines of similar capacity so you might check this out for the Nanni.You're increasing capacity anyway so you'll surely be having new systems incl inlets/seacock /strainers/trap /gooseneck etc. throughout in limited space.Another factor to consider.
 
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bluerm166 said:
Current Yanmar and Beta engines require larger diameter intake and exhaust than the older engines of similar capacity so you might check this out for the Nanni.You're increasing capacity anyway so you'll surely be having new systems incl inlets/seacock /strainers/trap /gooseneck etc. throughout in limited space.Another factor to consider.
Click to expand...

Thanks. I will keep what I can and replace what I have to. The exhaust system is 40mm from engine to water trap and 50mm thereafter, using a Vetus water trap with interchangeable inlets, so it may be possible to reuse that. I'd like to fit a new inlet seacock/strainer , simply because the old one is at the extreme end of what I (6'4") can reach. Of course that will depend on the shape of the new engine.
 
We have a Beta 14 (same base engine as the Nanni) in our heavyweight, long keel 23 footer. It is more than powerful enough. I would guess that 14hp would be sufficient for a 26 footer, 16hp (available from Beta, as mentioned, but not Nanni I think) would be ample, and 21hp a bit over the top.

I seem to recall that the alternator alone will usually take the first one horsepower, so the increase in power over your current engine will be more than the simple proportional increase of bhp.

While a triple may well be smoother than a twin, we have never perceived a vibration problem or irritation with our Beta 14 twin. (That's after clocking up over 500 hours use over the years, and numerous long runs including one of 23 hours continuous running.)
 
Prop size restriction aside, I don't think anyone ever complained about too much engine power, but not enough is a right PITA.

I'd fit the biggest possible that I could afford.
 
I've the beta 16hp in a 26', 4.5 ton long keel Nic 26. 1800rpm will do around 4.5 knots in calmish conditions & 2200 rpm will do just about 5knt . 2400 rpm will push me through the Portsmouth harbour springs ebb and 6knots comes up around 2800 revs. I've never had it up to it's max revs of 3600. This is with (I think) a 13x8 3 bladed prop. I took the 16 for various reasons at the time but I was originally sizing up the 14hp beta which I think would have been perfectly fine. 21hp in that size of boat just seems to me a tad oversized, I can't see you'll ever use it. Wiffling along at 1800 rpm on a flat calm it'll sip just over a litre an hour and noise and vibrations in such a small twin are minimal and I can't see a 21hp triple being noticeably smoother. The Beta is certainly quieter and smoother than the rigidly mounted, 9hp, single cylinder Sabb that it replaced (and easier to start, less smelly, easier to service, lighter.........etc).

Good luck with whatever you choose.
 
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