Hardy 20 Fisher Prop? Help!!

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shortless01

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We have just launched our Hardy 20 Fisher after 6 mounths of refit, toady we had our first sea trial.
Engine:Mercury 80 EFI
Prop: 17 Inch
Engine height: Will post later(Fitter said its a bit low!!)
Trim tabs: fitted and working
4000rpm:10Knts
6000rpm:14Knts
6000+rpm 17Knts Just getting on the plaine+ cavitation.
The engine over reved to 6500 rpm( Running in!!!)oops
Help!

Regrds
Shortie
 
welcome to the fora
Hardy owners club have a read thro' whilst waiting for the boffins to come along,prob seems wrong to me although the bofs will want the pitch of the prop as well eg 17 x14
 
Hi Shortie, again, welcome to forum.

Sorry, I'm not one of the experts that I am sure will post soon....!
...but do have some experience so I will give you my thoughts! IMO reading through what you have listed I believe a 17" pitch prop would have been about right.... I'm sorry to say IMO the root of the problem would be the engine being too low.

.... I do also recall someone else with a Hardy Pilot up in the Aberdeen area posting an issue he felt with speed / fuel consumption... and he was hoping a different pitch prop was the answer../forums/images/graemlins/confused.gif
I think the general opinion in that case was he either needed to shift any weight forward or get a bigger engine or just be happy at displacement speeds. But I think he was planning to re-prop... You never know maybe he will get in contact! I will have a look back in the postings... probably was around 6 weeks go....

I will just add, do like Hardy Pilot's, a nice boat!
 
.... just thinking about this while I took my dog for a walk and the issue of it cavitating and over-rev'ing would actually not be what I would expect if it the engine was too low.... lack of speed and performance would be...

...so as I said, I'm no expert!! /forums/images/graemlins/grin.gif

You may well be right, a different pitch prop might just be the trick. Certainly if its rev'ing well over 6k with a lack of performance you would need to step up to say a 19" pitch. But there is an ever increasing move toward 4 blade props... this coupled with a greater pitch might still give you the pick up you need for the weight of the boat, but give you increased topend at lower rev's... I will wait with interest too see if any of this makes sense to the real experts!!! probably not... /forums/images/graemlins/confused.gif
 
Thank you very much for your ideas
I just got off the phone to our engine supplier....
The engine is roughly at the right height but might have to be lowered! The prop size is correct for the boat, My feelings are to try a 19inch prop first then go for the engine position hassel.
This is becoming rocket science to me...no easy answers!!!
Again thanks for your thoughts
Shortie
 
[ QUOTE ]
The engine is roughly at the right height but might have to be lowered!

[/ QUOTE ]

Oh an engine being too high would over rev and cavitate...., too low it would lack power and struggle... try a prop first, its easy to do that, try and borrow one before buying! but if its too high then it is still going to have same problem. Keep us posted!! Good luck /forums/images/graemlins/wink.gif
 
When I bought my boat it had a 4 bladed (cant remeber the size) prop on it and was very slow to get on the plane, but got up there in time and reved all the way to the max. Moved to a 16inch which got on the plane like a rocket but top end was down, but have now moved to a 19inch to get the best of both worlds. But I have a searay with an inboard. Thought this might help to let you know that props may be a good way to go for now IMHO
 
get the engine height right first then test her again,then worry about the prop.On the HOC with a 75hp 4 stroke they recommended a 13 3/4 x 13 prop
 
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