Laysula
Well-Known Member
We had a Hanse 301 with a 10hp Volvo engine. Perfectly adequate as long as the bottom was kept reasonably clean.
Re-engine 28 foot boat - 14 hp enough?
- Thread starter neil_s
- Start date
jamie N
Well-Known Member
Tranona
Well-Known Member
Maybe, but when either ordering a new boat or replacing a old engine you have the opportunity to have better than "adequate". It seems perverse not to take advantage of the choice.
Tranona
Well-Known Member
When you enter the data for thee Seal 28 you get exactly what I suggested in post#53 Pretty reliable programme and similar to that used by many in the trade.
LittleSister
Well-Known Member
Ah, yes, I'd forgotten that aspect of it. Will the BW6 not fit on the Bukh DV24?
Beta will make you non-standard feet to fit a Beta to your existing bearers. I think the additional cost of a Beta 16 will only be a few hundred quid more than the 14, and worth it, both for the extra 'spare' pair off horse and to make any future sale of your boat easier.
That's too expensive for a second-hand motor, in my view.
Beta used to do 'Boat Show' offers in winter.
alahol2
Well-Known Member
They would also 'negotiate' some extras eg shallow sump option at no extra charge, upgraded instrument panel at no extra charge etc.
If you don't ask you don't get...
doug748
Well-Known Member
I should add that I have owned two boats, one with the 20hp and another with the 14hp Beta this year!
The 14hp was in a boat not dissimilar to the OP, 27ft about 21/2 tons. That boat absolutely flew with it's 14hp, at tick over it was cracking along. Coming into a berth you had to knock it out of gear in order to get below 2 kts.
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The 14hp was in a boat not dissimilar to the OP, 27ft about 21/2 tons. That boat absolutely flew with it's 14hp, at tick over it was cracking along. Coming into a berth you had to knock it out of gear in order to get below 2 kts.
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Poignard
Well-Known Member
Same with my Twister, with its 10hp BUKH. In and out of gear to go slow!
Tranona
Well-Known Member
That suggests you have the wrong propeller with too great a pitch. Nothing to do with the ultimate power output of the engine but how far the boat moves for every revolution of the shaft. At very low speeds like that the power requirement is minimal - less than 1hp
Some bedtime reading for you (and others) who want to understand the principles of small boat propulsion. scribd.com/document/190370044/Propeller-Handbook
doug748
Well-Known Member
Wrong pitch or not it was not short of power, the OP will no doubt be better guided by practical experience and the ten or so assurances he has had that the 14 hp engine will be grand on his boat.
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Blueboatman
Well-Known Member
I will add a bit of confirmation bias now that the OP has got this far.
If the s/h engine that promoted this thread is priced at half of the cost of a new one yet is ‘ somewhere’ in its second half life of wear
, clearly the smart money is on buying new and enjoying trouble free motoring before selling that engine in 10 or 15 years time for half of its replacement cost . Man maths
Myself, the only s/h auxiliary I would ever have considered ( and they were pretty much a drop in replacement for my last 3gm30F, which actually was fine) would be one of those ex lifeboat Yanmars that used to come up every so often with Marine Enterprises under their old management .
Now those really were low hours engines , for better or worse !
If the s/h engine that promoted this thread is priced at half of the cost of a new one yet is ‘ somewhere’ in its second half life of wear
, clearly the smart money is on buying new and enjoying trouble free motoring before selling that engine in 10 or 15 years time for half of its replacement cost . Man mathsMyself, the only s/h auxiliary I would ever have considered ( and they were pretty much a drop in replacement for my last 3gm30F, which actually was fine) would be one of those ex lifeboat Yanmars that used to come up every so often with Marine Enterprises under their old management .
Now those really were low hours engines , for better or worse !
Laminar Flow
Well-Known Member
As Tranona points out, it is not about hull speed per se.
The loading of a diesel engine should be as follows and as a percentage of engine RPM.
Economical cruising speed is between 45% and 65% (max)
The highest cruising speed in an emergency would be between 65% and 80% of nominal RPM.
Other than for short bursts, anything over 80% should be avoided.
An over-propped, new engine not capable of reaching it's max. nominal RPM, voids the warranty.
Industrial engines and those operating under heavy load are factory throttled to 60% of their potential output.
A larger engine running at reduced RPM is quieter, more economical and lasts ages longer.
Power is not simply about whether a boat can travel at nominal hull speed, but, more to the point, whether she has sufficient power to punch through a head sea in adverse conditions and get you home safely. In these conditions, an over pitched prop will overload the engine, causing glazing and an early death, not to mention the voided warranty when that happens.
On used marine engines, even ones with low hours: most marine engines are sat to death, rather than run to death.
The loading of a diesel engine should be as follows and as a percentage of engine RPM.
Economical cruising speed is between 45% and 65% (max)
The highest cruising speed in an emergency would be between 65% and 80% of nominal RPM.
Other than for short bursts, anything over 80% should be avoided.
An over-propped, new engine not capable of reaching it's max. nominal RPM, voids the warranty.
Industrial engines and those operating under heavy load are factory throttled to 60% of their potential output.
A larger engine running at reduced RPM is quieter, more economical and lasts ages longer.
Power is not simply about whether a boat can travel at nominal hull speed, but, more to the point, whether she has sufficient power to punch through a head sea in adverse conditions and get you home safely. In these conditions, an over pitched prop will overload the engine, causing glazing and an early death, not to mention the voided warranty when that happens.
On used marine engines, even ones with low hours: most marine engines are sat to death, rather than run to death.
Tranona
Well-Known Member
You cannot change the physics and a 14hp will not have enough power to achieve what the boat is capable of achieving. He currently has a 20hp engine which is marginally overpowered, but he would like to use his current propeller and he needs a 20hp for that. His boat is 700kgs 30% heavier than yours and has a longer waterline length so any comparisons with yours are not helpful. Your boat will achieve hull speed comfortably with 14hp but the OP's will not - it needs the extra 20% or so hp plus an appropriate propeller. Exactly as I suggested in post#53. If I were doing this job with this boat my choice would be the 16hp with a TMC40 2.6:1 reduction and a 15" 2 blade Flexofold. which would be much the same cost as a 20 without propeller
You only seem to read the posts that agree with your narrow view and there are just as many on this thread advising that a 14 is underpowered and a 16hp is the minimum based on both the calculations and personal experience. If you read the book and do the sums you will come to the same conclusion
If you fit a larger diameter smaller pitch propeller to your boat you will reduce the excess speed of the boat at tickover and probably increase maximum speed as it may not reach full rpm with the current propeller. Some people like to overprop in the belief that it is good for the engine but one of the penalties is excess speed at low rpm. "Not short of power" is meaningless - your engine is rated at 13.5hp at 3600rpm and at tickover (800) it produces 2hp. The starting point of deciding on powering a boat is the propeller then working back to a shaft speed and power to turn that propeller. It is not difficult to get it right by using the free propeller calculators such as Vicprop
neil_s
Well-Known Member
The TMC 40 gearbox with 2.6 reduction would fit into my hull and allow the Beta 20 motor to fit into the engine space - but Propking says I would need a 15 X 9 prop. 2.8 reduction is necessary for the 16 X 10. Sorry - I must have fluffed the calculation first time around - the 16 with TMC 40 needs a 14 X 8. and 15 X 9 with the TMC 60. I would like a folding prop, but I have the rudder skeg immediately in front so no room for the blades to fold. I have a two blade prop at the moment. I will talk to Beta around both 20 and 16 motors. The idea of the 14 was only born out of the e-bay advert. Thanks to all! much appreciated!
Sea Change
Well-Known Member
What about a feathering prop?
doug748
Well-Known Member
Not meaningless at all, a bizarre comment.
The OP has a small, light boat, the guy says he sails in protected waters, 5 kts is his preferred speed, he says he is not interested in offshore sailing. Answer his question instead of trying to impress everyone.
The boat in question performed very well with it's 14hp, that is all the practical information the OP needs. The internet is full of tap room experts on every subject you care to mention, many of them more interested in arcane argument rather than actually getting on with matters.
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Tranona
Well-Known Member
It is also has its fair share of people who seem to have little understanding of the subject and dismiss anything that has a sound basis in the underlying principles.
It is not a "small light boat". It displaces 3.2 tonnes and should be powered to suit. It does not perform "well" with 14hp - it currently has 20.
The information he needs is that which gives him the optimum performance. He will be spending close to £8k so needs the best advice not secondhand opinions.
As you see he is taking the sensible route of consulting professionals he do understand.
Tranona
Well-Known Member
You don't need a TMC60 . That is only needed when you get to or above the 30hp. The different prop size will be because there are different reduction ratios available. The 40 has 2:1 or 2.6:1 The 2:1 would have a 14" 2 blade on a 20hp and a 15 or 16" on a 2.6:1 Your 16*10 2 blade would work but might need repitching back an inch or so. The only downside with the 40 is reverse is 2:1 irrespective of forward ratio which means it can be a bit fierce in reverse. You can mitigate this by fitting a Featherstream 3 blade which has the option of different pitches in forward and reverse, although expensive.
A 16 will just about make hull speed at 6.8 knots and the 20 make 7.4. The big difference is that you will be able to cruise at 2-300rpm lower for your 5-5.5 knots. fuel consumption will be essentially the same with either option as the power required and therefore fuel burned will be the same.
As I have suggested in other posts propeller choice is probably more important than engine choice. Generally larger diameter and blade area is better for motoring performance and as you seem to have clearance to use a 16" it make sense to aim for this. You can get 15" with the 16hp.
Good luck with your pondering! At least now you can quantify the pros and cons.
Ceirwan
Well-Known Member
I had an MGC27 with a Penta 2001, 9hp. It never made full revs, (not over propped, just old) but was reliable.
Could motor at over 6 knots in flat water, and reliably at 5/5.5 depending on the conditions.
I think for the OP 14hp will be perfectly adequate, any more than that is a personal preference but with added weight & usually a little bit more cost.
jamie N
Well-Known Member
It's quite clear that the 'knowledge' and proven formulae shown so far do give a very narrow width of results, which makes the choice easier. If the OP fits a lighter engine, be it 14HP or 20HP, he'll be better off on purely 'power to weight'. With the more powerful engine he'll be more able to maintain hull speed against a stronger wind, and will be even better having a matched prop, and better again across the whole spectrum of the sport if he's got a folding/feathering prop.
My GK24 has a 6hp outboard, great in flat water where I can get hull speed, but against any sort of wind the speed drops in a fairly linear fashion, and with waves even more so. However the GK24 is a lightweight sailing boat, which isn't too arduous to sail, so I'm granted more opportunities to sail, rather than motor, which is really why we're here.
Moving slightly further on, there was the case where the RNLI were called out to tow a boat that had lost its engine near Inverness last year? Not so unusual, what was difficult for me though was that they did the call from where they'd anchored, a long way from Inverness rather than sailing closer in as "the wind was from the dead zone"; a F4, on the nose.
This does seem to be the case that so many people eschew any sailing into a head wind. If there's any prospect of beating at all, the motor's on, which is part of the reason why the engine power issue is so frequently mentioned.
Each to their own, this is only an observation, not a criticism.
My GK24 has a 6hp outboard, great in flat water where I can get hull speed, but against any sort of wind the speed drops in a fairly linear fashion, and with waves even more so. However the GK24 is a lightweight sailing boat, which isn't too arduous to sail, so I'm granted more opportunities to sail, rather than motor, which is really why we're here.
Moving slightly further on, there was the case where the RNLI were called out to tow a boat that had lost its engine near Inverness last year? Not so unusual, what was difficult for me though was that they did the call from where they'd anchored, a long way from Inverness rather than sailing closer in as "the wind was from the dead zone"; a F4, on the nose.
This does seem to be the case that so many people eschew any sailing into a head wind. If there's any prospect of beating at all, the motor's on, which is part of the reason why the engine power issue is so frequently mentioned.
Each to their own, this is only an observation, not a criticism.