fisher 25

G

gavin400

Well-Known Member
Joined
25 Aug 2009
Messages
426
Visit site
I've seen a Fisher 25 at the Scottish Boat Show which has a 20hp engine - I vaguely remember an article in a yachting mag many years ago which said that the 20hp was too small.

All advice gratefully recieved.

Gavin
 
Std engine in the 1990's was yanmar 3gm 27hp so it maybe slightly underpowered. If it throws a large 3 bladed prop it maybe adequate but only just. Plenty of earlier boats with 23hp Volvo's.
 
gavin400 said:
I've seen a Fisher 25 at the Scottish Boat Show which has a 20hp engine - I vaguely remember an article in a yachting mag many years ago which said that the 20hp was too small.

All advice gratefully recieved.

Gavin
Click to expand...

Hi Gavin

The Fisher 25 is not so far away in sizes/displacement etc to the Colvic Watson 23'-6", you will find the 20hp Yanmar engine will give a Fisher 25 a fair turn of knots and many of the Fishers have a 20hp engine fitted.

I have sailed a CW 23'-6" with a 20hp engine and again it will do the job, but where you will see the 'lack of power' is when you are in poor weather conditions or against a good current, I have two friends both with a Fisher 25, one has 24hp Yanmar and the other with 25hp Volvo engine and they cope with most weather conditions no problem with a good turn of knots, some have up to 30hp engines fitted.

My own CW 23'-6" has a 27.5 hp Isuzu Marine engine which is fine in all conditions so if you plan mainly for offshore use I would looks for a Fisher with around a 24/25 HP engine min.

Hope this might help
 
Driving a displacement vessel at more than hull speed takes a lot of additional power as much is wasted in cavitation, and creation of the wake. If you have a 25'vessel and you have a four knot current flowing against you, you'll struggle to make more than two knots over the ground. Where a little extra power comes in handy is when you're overcoming rough conditions or a headwind. Even so, I'd be reluctant to fit and use an engine with more than a 20% excess over that required to drive the hull at hull speed. I notice it's currently "fashionable" to over engine easily driven hull shapes. I suppose if you have a high electrical load and wish to drive a high output alternator, it may be acceptable to go a little bigger. I was advised to fit a 27hp engine to replace my old MD1b Volvo. I ignored the advice, bought a 1GM10 and it's quite capable of driving my 26'er at 6 knots, while charging two 80AH batteries.

It's very important to have a prop that is correctly sized for the engine/hull combination. Probably more so if your engine is marginal.
 
The spec. for this particular boat quotes 4/5 kts crusing, 6.5kts max. - so I suppose the engine size may be ok.
 
Topcat47 said:
Driving a displacement vessel at more than hull speed takes a lot of additional power as much is wasted in cavitation, and creation of the wake. If you have a 25'vessel and you have a four knot current flowing against you, you'll struggle to make more than two knots over the ground. Where a little extra power comes in handy is when you're overcoming rough conditions or a headwind. Even so, I'd be reluctant to fit and use an engine with more than a 20% excess over that required to drive the hull at hull speed. I notice it's currently "fashionable" to over engine easily driven hull shapes. I suppose if you have a high electrical load and wish to drive a high output alternator, it may be acceptable to go a little bigger. I was advised to fit a 27hp engine to replace my old MD1b Volvo. I ignored the advice, bought a 1GM10 and it's quite capable of driving my 26'er at 6 knots, while charging two 80AH batteries.

It's very important to have a prop that is correctly sized for the engine/hull combination. Probably more so if your engine is marginal.
Click to expand...

Considering that your old MD1B was 10 HP, I think you made the correct choice. 27 HP would be way over the top and you would have to have fitted a very much larger prop. Howver, in the case of the Fisher 25, it is a very heavy boat for its size and has a lot of windage being a ketch so I feel that 25HP would be right or a lower HP but with 3:1 redcution if there was room to swing a bigger prop, Lower prop speed would be less slip / caviation but more prop drag but then its a Motor Sailor
 
Last edited:
That's more or less the point I was trying to make. The fisher isn't a particularly easily driven hull and there is a lot of windage with the wheelhouse. Even so, I'd question the sense of fitting a 30+hp engine. Someone, sometime has to have done the sums so I may be wrong but I have sailed on a 57'cruiser fitted with a 36hp engine that would drive it at 12 knots.

BTW by the time it died, my old MD1b was probably putting out around 6 or 7hp. It still pushed Snark along at 5knots even then.
 
Maximum speed

Topcat47 said:
That's more or less the point I was trying to make. The fisher isn't a particularly easily driven hull and there is a lot of windage with the wheelhouse. Even so, I'd question the sense of fitting a 30+hp engine. Someone, sometime has to have done the sums so I may be wrong but I have sailed on a 57'cruiser fitted with a 36hp engine that would drive it at 12 knots.

BTW by the time it died, my old MD1b was probably putting out around 6 or 7hp. It still pushed Snark along at 5knots even then.
Click to expand...

The max speed for a displacement hull is = F X Square Root waterline length where F is between 1.3 and 1.5 with the later for a fine driven hull. So max speed for your 57 foot boat would be just under ~ 11.5 knots.
 
Topcat47 said:
That's more or less the point I was trying to make. The fisher isn't a particularly easily driven hull and there is a lot of windage with the wheelhouse. Even so, I'd question the sense of fitting a 30+hp engine. Someone, sometime has to have done the sums so I may be wrong but I have sailed on a 57'cruiser fitted with a 36hp engine that would drive it at 12 knots.

BTW by the time it died, my old MD1b was probably putting out around 6 or 7hp. It still pushed Snark along at 5knots even then.
Click to expand...

We have a Fisher 25 with a 27hp Yanmar and Brunton Autoprop. Usually run her at 5-6 knots at approx 2500rpm. The extra power in conjunction with the self pitching prop ensures she can make good headway in most weather.
 
Surely torque/gearing/prop is much more important than hp/bhp and it would be much better to have a high torque/low revving engine than a vehical derived engine that revs to 2500-3000 to get 5/6 knots. What is wrong with an old Lister, Kelvin, National or Gardner or even a 4D. I currently have 72' Barge with an aircooled Petter of 20hp which copes with anything that the Trent throws at it and a 33' heavy wooden cruiser with a 4D that easily coped with a little bit of the North Sea at 8/9 knots. I also previously had a 54' tug with a 27hp 3 cyl National which coped easily with the tidal Thames. They all use hardly any red - !/1.5 litres per hour and are extremely easy to work on. Common to all is that they are all slow revving 400-1000 and have masses of torque especially the National.
 
cavitation said:
The max speed for a displacement hull is = F X Square Root waterline length where F is between 1.3 and 1.5 with the later for a fine driven hull. So max speed for your 57 foot boat would be just under ~ 11.5 knots.
Click to expand...

There's so much myth about "displacement" speed - to call it maximum speed is I'm afraid a complete misunderstanding of what it means.
 
cavitation said:
... it is a very heavy boat for its size and has a lot of windage being a ketch ...
Click to expand...

Being a ketch has nothing to do with it! The topsides have the windage of a block of flats and the hull has immense drag for a boat of this size - that's what requires over twenty horses to drive something the length of a rowing boat.

Rob.
 
Lazy Kipper said:
There's so much myth about "displacement" speed - to call it maximum speed is I'm afraid a complete misunderstanding of what it means.
Click to expand...

There is no myth there is a very good scientific principle if I recall to do with wave lengths in water or something. Which Makes 1.34 x sqrt waterline length in feet the formula.

The fact is a good boat designer will know how to cheat and make a hull form that is not so restricted by this formula.

Wiki is quite good on the explanation and I would hazard a Fisher is not desgined to cheat any of the rules, she is a displacement hull. So will be very hard to push past those limits.
 
onesea said:
There is no myth there is a very good scientific principle if I recall to do with wave lengths in water or something. Which Makes 1.34 x sqrt waterline length in feet the formula.

The fact is a good boat designer will know how to cheat and make a hull form that is not so restricted by this formula.

Wiki is quite good on the explanation and I would hazard a Fisher is not desgined to cheat any of the rules, she is a displacement hull. So will be very hard to push past those limits.
Click to expand...

+1,

I discussed this factor with several boat owners who also happened to be fighter aircraft designers.

The Fisher 25 was always a lemon, also marketed with a vaguely streamlined top as the ' Freeward 25 '...:rolleyes:

Re propulsion, it would require something like an RB211 jet engine or a hurricane from behind just to get the thing to hull speed ! :)
 
Please reread my post - we all know about displacement speed and understand it's basic principle. As you rightly say it can easily be cheated and is only a guide - it does however have several myths attached to it and what it most emphatically is not is a maximum speed which once you've re-read my post you will see is the only point I made.
 
Seajet said:
+1,

I discussed this factor with several boat owners who also happened to be fighter aircraft designers.

The Fisher 25 was always a lemon, also marketed with a vaguely streamlined top as the ' Freeward 25 '...:rolleyes:

Re propulsion, it would require something like an RB211 jet engine or a hurricane from behind just to get the thing to hull speed ! :)
Click to expand...

PN numbers:

Westerly Centaur: 1203

Fisher 25: 1113

Such preconceptions :D

The Anderson 22 comes out a little better though at 1063, almost as fast as Heavenly Twins at 1034
 
Lazy Kipper said:
PN numbers:

Westerly Centaur: 1203

Fisher 25: 1113

Such preconceptions :D

The Anderson 22 comes out a little better though at 1063, almost as fast as Heavenly Twins at 1034
Click to expand...

I know friends - good sailors - who were misguided enough to get a Heavenly Twins; it sat in the sea like a pudding going nowhere and they got shot of it quickly...

Please do come along on any trundle - - or our club race,I'm mentioninng a berth on my boat for you seriously, you are welcome to come back here and report your findings ! :)
 
You must log in or register to reply here.

Other threads that may be of interest

Y
The Seafarer 700 and NASA clipper sounders saga
Replies
10
Views
430
Dellquay13
Dellquay13
R
Brokers.
Replies
6
Views
458
Irish Rover
Irish Rover

Share this page

Top