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Message board > Engines > Navigator + Mariner 60 HP (4 stroke) ... What prop size?

Message 8 of 8
Posted by member Andy Mcmullan on Saturday 11 December 2010

Hi John Last year I put a spare prop on my Yam 80 and found that the engine would rev but I had no drive worth talking about. I took the prop off and threw it out thinking the rubber hub was shot. When I bought a brand new yam prop I realised that there is a separate part that goes between the prop and the hub that was stuck fast to the old prop when I took it off. That was what was wrong with the spare I threw out. Could it be that there is some issue with how the prop is fitted? Not sure if Mariner is the same but is there any chance that there is a sleeve like part missing? If the prop tightens down correctly with the lock nut and the prop still spins ok by hand when in neutral, and locks up frimly when the engine is in gear and doesnt slip if you lean on it a bit, then I suppose it's likely fitted ok? A long shot but thought I would mention it just in case. Cheers, Andy

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Message 7 of 8
Posted by member Jon Dalton on Thursday 9 December 2010

Thanks Simon, I agree entirely that the problem must be something fundamental. The rubber hub within the props that I have tried have been bonded ok there is evidence of slip. The rev counter was set to 4 cylinder and 4 stroke. By ear I can tell the revs reading on the counter are true for what the engine is putting out. The wire feed that supplies RPM signal to the counter is a single wire, so I very much doubt that there is a return signal to the engine management system. Just to make doubly sure, I disconnected it - no difference. Intially I doubted the EFI module on the outboard. The 60HP has an engine block that also serves the 50HP and 40HP. So I wondered whether the lower rated EFI unit had been wrongly installed. But the EFI unit states 60HP on the manufacturers label that is stuck to it, so should be correct. The underside of the boat is slimey but not weedy. While she is out of the water for antifoul etc., I shall get the engine supplier to rig up a diagnostic computer to the engine. My suspicion is that the computer EFI is at fault - I will report back. Unfortunately the boatyard that supplied the Mariner outboard (from new) are not very savvy about engines, and are pretty much indifferent about the poor performance of the boat & outboard!

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Message 6 of 8
Posted by member Simon Kidd on Monday 25 October 2010

Hi Jon, I've had many years happy boating with a Hardy Navigator (no. 1404) Was "Caroline", now I think shes called "Calypso" and is somewhere in Newhaven I think. - in this case with a 50hp Mercury 2-stroke (1986 engine). She would easily exceed 20 knots, so yours should really fly. Normally the weight would need to be brought forwards, i.e. if 3 or 4 up, everyone at least as far forward in the wheelhouse as possible. (Once on the plane, usually you can move back again - four strokes are heavy, so unless you use trim tabs, this may be needed). Really, the company who supplied and installed the engine should be able to help you out here. The performance problem is really significant, and the changing of props through my experience is more about fine tuning - i.e. propping for fast acceleration (under-propping) or higher cruiser speed (towards over propping). Your problem could be something much more fundamental. My first thought was, is the rubber hub within the prop bonded correctly to the prop? Though it looks as if you've used 2 props, so this should have been ruled out. My next thought is: Is the Rev counter set up properly? They usually has a switch on the back allowing you to select a setting correlating to the number of cylinders in your engine. I.e. rev counters usually have settings for 2, 3, 4, & 6 cylinder engines. Having the wrong setting selected will result in the incorrect revs being displayed. Do of course check with the supplier before changing. I'm not sure whether this would also feedback the revs to your engine causing it to limit at max revs?? (I'm assuming your engine has an over rev limiter, most do these days). If this rev counter setting is correct, the hull is clean (this is really important, slime and weed slow boats down hugely!!), the boat not over loaded, the engine trimmed down, the cavitation plate at the correct level (as above), and the prop hub in good condition, then I could only expect an engine electrical fault - again your engine should be under warranty if new and so the supplier should be able to check this for you. Good luck, do report back when the problem is solved!

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Message 5 of 8
Posted by member Jon Dalton on Thursday 23 September 2010

Thanks Damian The outboard is indeed a longshaft version, and the cavitation plate is about level with the bottom of the hull (that is to say level with the bottom of the hull at the stern). As far as I can tell from observation, the engine cannot be lowered any further. The splashwell transom height, engine, power tilt/trim unit and hydraulic steering limit the extent that the outboard can be lowered. If the prop was cavitating, would the stainless steel be pitted by now after a number of hours at full throttle? Thanks for your ideas!

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Message 4 of 8
Posted by member Jon Dalton on Wednesday 1 September 2010

Thanks Clive. Your post agrees with the general comments I get are that the boat should 'fly along' with a 60Hp outboard. I have put a 10-and-a-quarter x 15p prop on and she will reach 9.5 knots and max revs that be be reached are 5,750 RPM at this speed. I will look into the height that the motor is installed on the transom and report back.

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Message 3 of 8
Posted by member Damian on Wednesday 1 September 2010

That engine should have power trim/tilt and it seems to be revving out to get the correct RPM at wide open throttle. Drop the engine right down so that it can go no further and try it. The original prop should be suitable for the boat. Is it a longshaft or short shaft engine you have fitted? This boat needs a longshaft. The cavitation plate above the prop needs to be level with the bottom of the hull.

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Message 2 of 8
Posted by member Clive Watkins on Saturday 28 August 2010

Sorry, I only visit the forum occasionally. I have a Merc F60efi, (which is I believe basically the same motor as yours - non bigfoot) on my Navigator 18. I swapped out a honda 45 Is your motor set too high on the transom. I reckon your prop must be ventilating/cavitating an awful lot for 9 knots at 6000rpm, otherwise you simply would not get to 6000rpm. With 2 adults, 60 litres fuel, 26kg auxiliary motor, plus 2m inflatable tender under the cabin bow seat, my setup produces 24.5 knots (via gps) at 6000 rpm with a 10.75 X 12 aluminium prop, and she is quite quick to plane either with doel fins or smart tabs (but bad without), and will stay on plane down to 12 knots.

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Message 1 of 8
Posted by member Jon Dalton on Sunday 7 March 2010

I have had a new Mariner 60 HP EFI (4 stroke, NOT Bigfoot) fitted to my Navigator and can only get 9 knots at 6000 RPM. The prop as supplied is a 10 and 3/4 x 12" three blade. The gearcase on this outboard is a 3 and 7/16" (87mm), and I believe therefore the shaft to be 13 splines. With the smaller gearcase I am limited in terms of diameter & pitch much beyond the prop supplied as above. Has anyone encountered similar, or any advice would be gratefully received. I'm now thinking that I should have gone for the 'Bigfoot' model!

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