steveeasy
Well-Known Member
A beta 14 with the right prop will be perfect for a 2.5 tonne 28 ft boat. My Twister was a fair bit heavier and with same hp with the right prop had plenty in reserve for anything.
Steveeasy
Steveeasy
Re-engine 28 foot boat - 14 hp enough?
- Thread starter neil_s
- Start date
Tranona
Well-Known Member
But the boat in question is not 2.5 tonne but 3.2 tonne. You cannot power the "correct" propeller with that hp (actually 13.5). You can't wish the laws of physics away no matter how hard you try.
Your Twister is not a good example. First it is 4.5 tonnes and cannot use the correct prop because the aperture is not big enough. The ideal propeller is 15" diameter and you need 22hp to achieve hull speed of 6.3 knots Most are fitted with smaller engines because there is not room for the ideal propeller. It is quite possible to be satisfied with lower power - I had over 20 years of underpowered boating and just like others posting on here managed fine. You work with what you have. However once you have experienced a properly powered boat you would not want to go back. In many cases like your Twister and my Eventide it is not possible to fit the correct engine/prop, but the OP has no constraints at it really does not make sense to spend that amount of money and end up with a sub optimal result. The decision might be different if he does not want, or can't afford new and if the 14 is good and has the right gearbox it will certainly power the boat in "normal" conditions and cost £3k or so less. but it will be a big step down from his current engine.
Snowgoose-1
Well-Known Member
Perhaps things changed when the Westetly Centaur started to have 25hp and 23hp Volvo's fitted. Even 30hp Watermota in some. Unheard of at the time. Perhaps this contributed to it's success. My wife , God bless her, loved to here the motor being started.
neil_s
Well-Known Member
My Bukh DV20 (maybe no longer in the best of health) with 2.5 : 1 ratio gives 6.5 knots flat out with the 16 x 10 2 blade prop. I don't know if it is getting to top rpm of 3000, though. We are making serious waves at that speed. Propking confirms the 16 x 10 as the ideal prop and also agrees on the top speed. It is a working set-up. I have to say I don't want to spend £8000. Restoration of the Bukh? It has low oil pressure, is a bit slow to start, has rattly valve gear and is obsolete and very heavy. Maybe talking the same money! Off to talk to the local Beta agent !
Tranona
Well-Known Member
That came about for the reasons I suggested earlier. The Centaur originally had the MD2 at either 13 or later 15hp, neither of which were powerful enough. The next up in the Volvo range was the MD11 which was too much but Volvo did a deal to keep the business from Bukh who could offer the 20. By the end of the 70s Volvo started to produce their own high speed diesels like Yanmar and gradually the options widened but too late for the Centaur
Beta 20 is commonly fitted as replacement - well matched.
Keith 66
Well-Known Member
Our Sabre 27 is 3.25 tons, fin keeled version. There are around 5 Sabres in our club. Most of her bilge keeled sisters are fitted with 18-20hp three cylinder engines, mostly Beta, Nanni, Yanmar. Ours has the Beta 16, we find it perfectly adequate, Prop is two bladed & could do with an inch more diameter but it works & was free. We often have to punch out of the creek against the tide & wind during the summer & the bigger engined bilge keeled sisters do have an edge on speed under power. However turn the engine off & the difference in performance is marked. the lack of drag from a big three bladed prop is noticeable. She is a sailing boat after all!
steveeasy
Well-Known Member
Hi,
Sorry are you saying this 28 ft boat that weighs in at a mere 3.2 tonnes needs a 20 hp engine. The laws of physics may well say so, but I can’t see any reason this little boat needs an engine the same size of that in my Contessa 32 that is nearly twice the weight.
My Twister at 4.5 tonnes had a Yanmar Ym 16 and had the correct size and pitch prop. She did not achieve full Hull speed. I decided to go with a greater pitch prop despite being told it would not work. The physics dictated so. Well it did work. The boat easily achieved Hull speed at the right engine RPM.
Twisters were fitted with 10 hp engines and although not over powered, owners seamed to find them satisfactory. Then owners started fitting 20 hp engines in them and they are certainly not underpowered but could be argued over powered. If the correct size prop can’t be fitted then increasing the pitch can be increased to counter this.
Might not stack up on paper but achieves what the users is trying to achieve.
Steveeasy
Edit
I note your final comments and so I’m not sure we are too far apart. If your will to spend big bucks get it right. If not perfectly good compromises exist.
Last edited:
Tranona
Well-Known Member
First the Contessa is actually lighter than the Twister by about 200kgs if all the published information is correct. No, I did not say the OPs boat needs 20hp. I said several times it needed a minimum of 16hp, whereas others claimed that the 14 originally suggested was "adequate". The owner currently has a 20 because when the boat was built the choice was either an underpowered 10 or a 20. He was also hoping to re-use the 16" propeller currently fitted.. Little cost or weight penalty and a smoother 3 cylinder rather than 2. Other owners had also fitted Beta 20s.
A boat like your Twister of 4500kgs needs 21hp to achieve the hull speed of 6.3knots Your 2Ym15 will give a maximum of 5,6 knots There is not a "right" propeller that will do better than that. Having a steeper pitch prop will reduce revs and only increase speed if the original prop was so fine that the engine achieved maximum revs before maximum speed. Have a look at the numbers here
Vicprop - Prop calculator for Displacement and semi-displacement hulls Better than a 10hp of course, but even a 20hp will not quite reach hull speed vicprop.com/displacement_size_new.php?action=calculate and even then not sure there is enough room to fit the best size propeller.
I cannot stress enough that achieving hull speed is used as an indicator of the power required to allow a comfortable cruise speed in the part of the power curve where the engine is at its most efficient. 5 knots in your Twister needs 10hp which the YM 15 does not produce until near 3000rpm and burning nearly 2l/h whereas a Beta 20 produces that at 2200rpm and just over 1l/h. Have a look at posts 35 and 72 for a fuller explanation. The choice of engines etc 50 years ago was nothing like it is today and boats were not designed for good motoring. My 1963 Eventide 26 (3 tonnes) had a Stuart Turner P55 8hp and ignoring the fact that it was smelly, dangerous and only worked when it felt like it enabled me to cruise all around the Channel and N France, CIs etc for the first 12 years of ownership until I fitted a 1GM which was a bit faster but crucially worked when I asked it to. Like the early Twister owners I found it "very satisfactory" despite a maximum of 5.5 knots and cruising at a screaming 3000rpm
It is not always possible to fit the correct size engine or propeller in a boat, particularly older boats - my Eventide for example needed major mods to the cabin layout to fit the 20hp it really needed, although I did change to a Nanni 14 which was virtually the same size as the Yanmar - but for many replacing engines allows the opportunity to take advantage of the wider choice to match the engine and propeller to achieve better more economical motoring. In some cases like the later Centaurs the better choice is a smaller, lower hp than the original.
ridgy
Well-Known Member
Sorry to reopen what was a lively thread but if the OP was to join the Boat scrapyard and lonely boats Facebook group, there are a number of px engines available including a beta 20 with an alleged 1500 hours for about £1800.
neil_s
Well-Known Member
Thank you for that tip! Not currently a Facebook user but will have a look. I would much prefer to go second hand if a good motor is on offer. I'm trying to not rush into this - there is a lot to weigh up. The old Bukh DV 20 has had it's winter service!
ridgy
Well-Known Member
Blueboatman
Well-Known Member
But is that replacement control panel @ some time in the engines life with its own hours? Who knows and how would you know except by inheriting the boats documentation and service paperwork and bills and and …
Getting old I am!
neil_s
Well-Known Member
Thank you, Ridgy, I've saved that to favourites.
ridgy
Well-Known Member
Any used engine is a risk, as already discussed above why take it out in the first place. My greek share boat has nearly 7000.hours on its Perkins M20 and still runs great. The engine in my UK boat is a 40 year old 2GM and still runs great. It it was me I would make arrangements to go and see it in person and observe it start and run from cold. It's a current model with spares availability, it's probably fine. Looking at their other adverts they seem honest about faults.
Blueboatman
Well-Known Member
I agree
Cold start and state of the mounts and ancillaries and exhaust
Still seems a lot of dosh for an old engine wrt to effort to put a new engine in ..
Fussy aren’t I?
Keith 66
Well-Known Member
Re Any used engine is a risk, True but in todays world with yacht values at rock bottom bargains are to be had.
I know of three boats in our club alone in the last few years that have been bought for less than 1k, One had a vetus twin in it, another a Beta12, another a Beta 18, two less than 50 & one that had less than 20.
All those boats had new engines fitted within the last ten years but owners get old & the boats were not used.
One boat was scrapped, another is about to be & one is in commission.
I know of three boats in our club alone in the last few years that have been bought for less than 1k, One had a vetus twin in it, another a Beta12, another a Beta 18, two less than 50 & one that had less than 20.
All those boats had new engines fitted within the last ten years but owners get old & the boats were not used.
One boat was scrapped, another is about to be & one is in commission.
Blueboatman
Well-Known Member
Yup, sounds sadly likely .
Always know the specific provenance then.
Local boatyard word of mouth I like
neil_s
Well-Known Member
Hmm - I guess I might be heading for that scenario. I did a lot more sun-bathing and tea drinking this last season than I did sailing - or motoring for that matter. At least that was on the mooring or close by! I am heading past the local Beta agent this afternoon!