Quicksilver 640 Pilothouse

[Member Removed]

Hi all new member to this site and was wondering if i could pick your brains,purchased a quicksilver 640 pilothouse in september and the engine will rev out to only 4300 revs with 19p prop, at 1st service dealer changed prop for 17p brining revs up to 5000,i have been told to maybe raise the engine 1 knotch (at moment is on the lowest setting) although the cav plate is level with bottom of keel,also another member says he gets 30+ knots with a 90hp mariner 4s on same boat,i have a 115hp mariner 4s and best top speed fully trimmed is 29 knots on gps and f/finder.

Any info would be handy as i feel i am perhaps not getting full speed from my engine.

 

thank's in advance Jim

 

ps i am away on a course all next week so sorry if i don't respond quickly

[duncan]

welcome Jim

 

What is the recommended WOT revs for this engine? Suspect you should have a similar rev and prop to you M8 - what is he running as a prop and what revs is he getting?

 

When you talk about bringing it up a notch - surely its got power trim and tilt?

 

Are you triming out to the optimum position once up and running?

 

Finally, and plese don't take this too personally - but are you and your gear a few kg more than him? As an example on my previous boat (6.6m) my son could get 4 knots more than me!

[Newboy]

You need to find out from the outboard manufacturer what is the max rev, on that model. It then need to be matched to a prop which will give you that max rev.

 

When you said moving up a notch, did you mean the different fixing holes?

[Member Removed]

Thank's for writing back,max engine revs 6000 according to mariner,height adjustment is via holes on outboard bracket,the guy with the other 640 was on another wesite that i cannot sign up to,it just seem's that i am probably not getting full hp only running at 5000 and was wondering if anyone has the same boat with similar setup.

Off on a course now,back on line Saturday.

Cheer's all

[Adam F]

Kwango,

 

We used to have a 640 and 115hp Mariner in the club until last year, the the max he had from it was about 29 knots I think.

 

The WOT throttle shoudl be 6000 RPM I would have thought, but most set them up to 5500 ROM, as you will be aware each 1" in prop reducetion should give a 100 RPM increase, but as your figures suggest your prop would be tiny by the time you reached this!

 

I can olny suggest speaking to Quicksilver and Mariner (dealer).

 

Finally, Mark (former 640 owner) had problems with the throttle cables sticking and this meant he couldnt reach full throttle - just another idea.

 

Finally - if you are getting 29 knots at 5000 RPM, I wouldnt be too dissapointed, the engine wont be running flat out like this at least. My Mariner (60hp 4 stroke on a Warrior 165) runs WOT at 5500 RPM which I can live with as the engine is not being hammered then.

 

Adam

[Nipper]

hi kwango

 

thats right yes i did have a 640 and i had about the same has your self out of the engine and the 115hp weights a lot more than a 90hp thats why the boat with the 90hp is faster but on the bright side the fuel saveing is alot greater with a 115hp and i also had problems with my thottle cables when replaced i could take the engine to 5500revs and still get between 29 and 31 knotts any problems give us a call .

07966 198093

mark b

[duncan]

Finally - if you are getting 29 knots at 5000 RPM, I wouldnt be too dissapointed, the engine wont be running flat out like this at least. My Mariner (60hp 4 stroke on a Warrior 165) runs WOT at 5500 RPM which I can live with as the engine is not being hammered then.

 

sorry to be a broken record on this but the boat should be propped to within 200 rpm of the engines rated WOT normally loaded for optimum

1. fuel economy

2. engine wear

3. transmission wear

4. top speed

 

On these larger engines, and especially 4 strokes, 400 or so off fully loaded is considered OK (especially if the engine is right at the top end of what the boat needs - Maverick's set up would be an example, Blue Warrior's not far behind in the ptw stakes) but at 1000 off you need to consider a different prop or something else is wrong somewhere. The other references to experiences here tend to suggest that that isn't the case unless it's down to the state of your hull or a 200kg weight box (don't laugh we weighed our weight bucket on Phaeton at 60kg last winter) Are you running a 'quality' prop - some of the cheaper stainless ones have such thick blades they can have the effect of seeming like more pitch without the advantages of it! You are fortunate in having pretty much lthe largest range of props made that fit your engine so something somewhere will be right.

 

the only thing you can really gain by not doing so is acceleration where significant gains can be made by using a lower pitch at the expense of 1, 2 and 4 above, and a need to take care not to exceed max revs with the throttle hand - in practice if you need more acceleration at the expense of 4 above moving to a 4 or 5 blade prop is the only correct route.

 

As an extreme example driving a car up a slope with your foot on the floor to just hold a higher gear do not deliver 1,2 or 3 above! An extreme to illustrate the point - the drag on a a hull means that boat engines are always driving up hill!

 

Top speed for any given craft is a product of hp so a higher gear (greater pitch) alone won't make your boat go faster and every OB I know produces it's maximum hp at it's max revs...........QED.

 

If you want to improve 1-4 above then don't whack the throttle open at every opportunity, cruise at 70-80% max revs if you can and change the oil frequently!

[great white]

Hi all

 

Duncan is right over prop an engine and the revs will be low as others have said

 

I" of prop is usually about 200RPM

 

but running a prop that is stopping you getting within 200 RPM of the stated Max RPM for the engine not good.

 

being able to get the correct revs but not using all that you have available is much better for the engine.

 

You have stated that a prop change has made a big diifferance I suggest try another prop.

 

Charlie

[Member Removed]

Hi lads at last back from the most boring course in my life,thank's to everyone who took the trouble to reply,your input really is a great help with some good idea's.

Thank's again Jim

 

[AlderneyBassman]

Hi Kwango,

 

I had the same problem of my new Etec90 maxing out at 4700 rpm. I had the engine up one notch and stupidly lowered it and the max revs went down to 4600

But more importantly, soon after I was steaming to a mark and all of a sudden the revs went soaring up to 6000 ish and we slowed down considerably

I thought the prop had dropped off

But as it turned out it was the prop bush that had failed.

So now with a prop with less pitch she reaches the 5000 rpm OK with some trimming, just got to raise it back up the 1 notch and it'll be fine.

 

So I would suggest raising yours 1 notch but more importantly look into a prop with less pitch before you shear the bush and have to limp home

[Member Removed]

Cheer's Bassman thought it might be worth raising the engine a knotch and you have confirmed my suspicions,will probably wait till next service and get the retailer to do it,free of charge he says,sorted.

Thank's a lot for that,safe boating

Jim