Wrong Propellor?

Hi Guy's; this is my first post and looking back through the posts I'm hoping that an expert can really help me here; so here goes;<br /><br />Mariner 40 Magnum 4 Cylinder, serial no; 09664785<br /><br />Driving a 16' Orkney Dory (think Dell Quay Dory but slightly different); Cathedral Hull forward, tapers to planing hull aft.<br /><br />Previously a rescue/patrol boat for National Park Ranger.<br /><br />Now we come to the tricky bit; when I bought it the propellor was found to be damaged and the shop replaced it free of charge prior to me getting the boat.<br />Propellor numbers are: 48 73134A40 12P<br /><br />But; the boat hardly goes onto the plane! The log says she's doing between five and six knots! My auxiliary Mariner 3.3 pushes the boat almost as fast! My suspicion is that the shop picked up a stock prop and stuck it on to save money and that they didn't do a like-for-like swap.<br /><br />Anybody got any ideas? Engine itself runs sweet as a nut apart from occassional misfire under load; compressions are all equal at 125psi, I've just run thru some Sea Foam type stuff and she idles better. My main concern is being unable to get onto the plane; surely the 40 Magnum should have us flying at around twenty knots plus?<br /><br />Any help/advice gratefully received,

Re: Wrong Propellor?

Welcome to the group! You will find a wealth of information here.<br /><br />The first question that pops into my mind when someone has a complaint about performance is "what is the wide open throttle rpm?". This engine should turn up to between 5000 and 5500 rpm at wide open. Also, you don't mention the weight of your boat so propping would be difficult at this point. A 12p prop may not be low enough to get the boat on plane. Let us know what the WOT is and we can go from there.

Re: Wrong Propellor?

Did it run good before they changed props? Did you drive it before you bought it? Does the engine "rev" up when you put the throttle all the way forward or does it just lug along? Thinking you may have a spun hub in the prop. Do you have spark on all cylinders? Good plugs? Prop pitch sounds right, so I would begin looking elsewhere for the problem. You may only be running on half the cylinders. This will not show up at idle with no load. Check prop for slipping, Check for spark, Replace spark plugs, Clean carbs if spark is good. This is why I suggest this:<br /><br />

Engine itself runs sweet as a nut apart from occassional misfire under load ; compressions are all equal at 125psi, I've just run thru some Sea Foam type stuff and she idles better.

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Re: Wrong Propellor?

sounds like 12" pitch is rather large - a friend had a Haines V133, 13.3' fiberglass hull with a 3cyl 65hp merc - that had a 12" pitch (although i cant remember the dia). check the WOT rpms first - that'll tell you if the bush is dead or not. the chances are that if the bush is dead and you have been running it under load, you will have damaged the hub of the prop, hence re-bushing will cause it to fracture. Also, if you have done the bush, i doubt that you'd even get it going at 6knts.<br />As i said though, first port of call is to check the rpms - that will isolate the prop rather quickly.<br />Andrew

Re: Wrong Propellor?

Even if the pitch is off a couple of degrees, the boat should do better that 5 or 6 miles per hour. I have a 16' Fiberglass Wellcraft runabout with a 28HP Evinrude on it and I run a 9" X 11" pitch on it and get 28 MPH and a great hole shot. So I can only assume with a 40 HP, that the 12" is close enough to get it going if everything is proper. I assume the prop diameter is around 12".

Re: Wrong Propellor?

Thanx guys! As far as I know, without a tacho WOT is 5500rpm. I didn't drive boat prior to purchase (fool!) She was at anchor and they (the shop) drove me to it on identical craft with identical engine; I was nearly thrown off with acceleration! But on our boat; a rice pudding hardly shudders from take off!<br />I used to drive inshore rescue craft for HM Coastguard and we used Mariner 25's that were so much faster! The boat is around 390Kg unladen suspect 700-800Kg laden; surely a Magnum 40 should get us on the plane?<br /><br />thanx for the answers so far

Re: Wrong Propellor?

Hey man, email me at www.greasemonkeyozi@yahoo.com about your problem.

Re: Wrong Propellor?

mercury.grease.rag <br /><br />Share you thoughts with us. We can all learn from others experience.

Re: Wrong Propellor?

Hey! Chris!<br />US Army or not; this is not a valid e-mail address; it takes me straight to a Yahoo website!<br /><br />Story so far; all four cyls are firing and WOT can't be measured (no tacho)<br /><br />Am I gonna have to buy a tacho to solve this problem?<br /><br />Bro<br /><br />Ex UK Royal Marine; if it makes any difference; respect advice about Sea Foam tho!

Re: Wrong Propellor?

Hey Bro,<br /><br />Can you answer some of the questions in my previous post and we can go from there. I know you don't have a Tach, but does it sound like the motor is "Winding out" when you hit the throttle and you are not really going anywhere?<br /><br />Like these previous questions:<br /><br />Did it run good before they changed props? Did you drive it before you bought it? Does the engine "rev" up when you put the throttle all the way forward or does it just lug along? Thinking you may have a spun hub in the prop. Do you have spark on all cylinders? Good plugs? Prop pitch sounds right, so I would begin looking elsewhere for the problem. You may only be running on half the cylinders. This will not show up at idle with no load. Check prop for slipping, Check for spark, Replace spark plugs, Clean carbs if spark is good.

Re: Wrong Propellor?

Rick,<br /><br />prop is brand spanking new; no hub slippage as far as i can tell.<br />The engine is firing on all 4 cyls and sounds like WOT is right.<br />Clean carbs?<br />Could fuel pump fault cause this ?<br />Was thinking about overhauling fuel pump; excessive thirst from this engine; 2 gallons per hour?? Is that right?<br /><br />cheers,<br /><br />Bro

Re: Wrong Propellor?

I'm sorry, I ment my email address is greasemonkeyozi@yahoo.com. I'm getting too frisky with my new dsl modem.

Re: Wrong Propellor?

Bro, theres something I want you to check out online, but I would rather not show you here. These forums are pretty strict when one gives the other too much help here.

Re: Wrong Propellor?

Sorry for delay in updating this thread; I took someone else's advice (the pub bore!!! doh!) and fitted a bigger pitch prop; the boat bogged down even more!!<br />So although it cost me money, I did discover that going down a size to 11" put me on the plane very quickly; anyone want to buy a variable prop (12" to 16" lol!!!)<br /><br />cheers and thanks for the responses

Re: Wrong Propellor?

Since the boat was moored...is the bottom full of barnicles and algie????? Run with the cover off the engine and squirt some fuel in the carbs @ WOT and tell us what happens. You should be running a 13" pitch prop with that rig...unless the foam is water saturated.

Re: Wrong Propellor?

FBM,<br /><br />suspect you are the closest to the problem! We have noticed that the boat is filling up with water whilst alongside; even with an auto bilge pump. She is coming out this weekend because the bilge pump is working so hard that the battery runs down in seven days; suggests major leak and like you say, waterlogged foam.<br />Will fix this for the next owner as I have found a supplier of RIB kits and have ordered one; so my boat will be sold minus engine,<br /><br />thanks for all responses!