arkedup Posted January 18, 2008 Share Posted January 18, 2008 hi all I am wondering if i should exchange my prop for 1 slightly smaller or different pitch ?? when i open the throttle it revs to about 5200 in perfect conditions if there is any wind and chop it will only rev to 5000 according to the book it should rev to 5750 in perfect conditions the motor is a new 115 optimax on 5.5 seafarer ventura it is using about 9.5 litres per hour according to total hours use divided by total fuel used it goes well other than its a bit slow out of the hole my dealer with some arm twisting said he will swap it once but if i am wrong i am stuck with it and if i want to go back to the size i had before i will have to pay for it and keep the smaller 1 am i expecting to much from it or will the right prop make the difference? Link to comment Share on other sites More sharing options...
pelican Posted January 18, 2008 Share Posted January 18, 2008 (edited) Outboards require the correct prop so they are under the right load at the correct revs as they have a fixed gear ratio. If you have the wrong prop you load the motor and it labours (like trying to go up a steep hill in 4th gear in a car) and this can result in internal carbon deposits , burnt pistons in the long term and more engine wear. In the short term the wrong prop will possibly use more fuel as the computers on the new outboards try and pump more fuel in at WOT to try and get to max revs. This is particularly important with 4 strokes as well as they often don't reach much of their rated HP until the upper reaches of their WOT settinngs so can be very slow to accellerate. To be blunt if it is a new motor and the dealer rigged it he should be giving you the right prop as he should be a professional and have a good idea. His choice - allow you to try several differeent props or do the bloody water tests himself- sorry getting old and grumpy. Props have many factors and the hull shae and weight will make every boat different. Load your boat up as it would be on a worst case and then do the testing. That way it will never struggle and overload the motor. Props can have different shapes for different purposes and suit different boats that require more stern lift etc Factors on props are number of blades Diameter pitch cupping blade shape rake of blades metal- stainless or ally or composite Some new motors do loosen up a little but nt sure about the optimax- seems too many revs to pick up unless you are running a run in mixture? Edited January 18, 2008 by pelican Link to comment Share on other sites More sharing options...
Flightmanager Posted January 18, 2008 Share Posted January 18, 2008 What size and pitch prop are you running? Ross Link to comment Share on other sites More sharing options...
a boat Posted January 18, 2008 Share Posted January 18, 2008 (edited) Hi Arked, on your boat and engine you would not more than the 16 inch Vengance prop. If you have an 18 inch it is too tall and ideally the revs want to be 5500 at least with your normal load. Pel is right, it is upto the dealer to fit the right prop for any boat and I think you should not have to pay for trying different props. The good dealers with any experience know what props work on what boats. Try a 16 inch and see what happens, the outboard will perform better if propped to reach 5500-5750 at WOT. Cheers, Huey. Edited January 18, 2008 by Huey @ Huett Marine Link to comment Share on other sites More sharing options...
arkedup Posted January 18, 2008 Author Share Posted January 18, 2008 hi Pelican thanks for your reply,so from what you have said in your reply it should have a different prop fitted to try to get closer to the wot rpm of 5750 that is what i thought but the dealer said that this is the prop that mercury recommend for this size boat I think i will ring mercury and see if they can help me cause the dealer is sure not looking after me here regards arked Link to comment Share on other sites More sharing options...
arkedup Posted January 18, 2008 Author Share Posted January 18, 2008 Hi Craig thanks mate once again i find myself wishing you were not so far away from me and i had bought from you ! regards arked Link to comment Share on other sites More sharing options...
GregL Posted January 18, 2008 Share Posted January 18, 2008 Im no expert but raising the motor sometimes gets more revs and more speed. Do you know if you can raise the motor a bit? I get about 500rpm with only a small adjustment of 3 holes on my jack plate. Is the motor bolted on threw the lowest holes? Might be something else to look at. Greg Link to comment Share on other sites More sharing options...
a boat Posted January 18, 2008 Share Posted January 18, 2008 Hi Arked, no problem, good point by Greg. In our experience the 3 cylinder OPTI like to run on the third hole, but I think also you want to make sure you have a 16 inch Vengence and that will be the prop to run. We are only 25 minutes from Gosford, so next time you go boating at the Hawkesbury swing by and say hi and I can give you my thoughts on the set-up of your outboard. Cheers, Craig. Link to comment Share on other sites More sharing options...
arkedup Posted January 18, 2008 Author Share Posted January 18, 2008 Hi Ross to be honest i dont know i think its a 17 or 18 i have sent a PM to craig with the no. in it Im sure he will be able to help If the no. means anything to you its a vengance 48-16988 18p regards arked What size and pitch prop are you running? Link to comment Share on other sites More sharing options...
IWANNABROCK Posted January 18, 2008 Share Posted January 18, 2008 Hi,I found this not sure if any help, The prop on my motor now is a Mercury Vengeance S.S. 48-16988 18P After much looking on the net I'm pretty sure it is a 13" diameter/18 pitch. I'm definitely interested in a vented prop since they sound good for what I need. Any suggestions? Link to comment Share on other sites More sharing options...
arkedup Posted January 18, 2008 Author Share Posted January 18, 2008 hi Greg there are 5 holes on the bottom of the mounting plate and the bolts are in the 4th holes from the bottom which brings the plate above the prop upto level with the bottom of the hull is that where it should be ? regards arked Im no expert but raising the motor sometimes gets more revs and more speed. Do you know if you can raise the motor a bit? I get about 500rpm with only a small adjustment of 3 holes on my jack plate. Is the motor bolted on threw the lowest holes? Might be something else to look at. Greg Link to comment Share on other sites More sharing options...
a boat Posted January 18, 2008 Share Posted January 18, 2008 Hi Grant, check your PM and yes you have an 18 inch, which is not the best prop for your Seafarer. A 16 inch would be the ideal prop for that boat/engine combo. As for the engine height, the top hole is No.1 and as I mentioned the 3 cylinder OPTI with the gearcase they run like to be on No.3 hole from our experience. That said I think the main prob you has it a too tall prop for a heavy deep veed boat like your Seafarer. Get them to give you a 16 inch prop, which is the coreect one and you will be where you need to be for better performance and engine life. As said in the PM if they do not want to help, I will give you the "Raider" deal on the correct 16 inch prop. Cheers, Huey. Link to comment Share on other sites More sharing options...
Little Hooker Posted January 19, 2008 Share Posted January 19, 2008 This could be off topic but says for a SS 16" prop what are they worth??? Im guess they get more $$ when you go bigger? Link to comment Share on other sites More sharing options...
a boat Posted January 19, 2008 Share Posted January 19, 2008 Hi Mate, no a 16 inch Vengance is the same price as an 18/20 or whatever pitch Vengance. The RRP is $950, better for Raiders. Different styles of props, like in the Merc range-Laser, High5, Trophy and the like can change the price, but most are under the $1200 (again the Raider price will be cheaper) and from our experience the BRP Viper, Cyclone, Renegade and the like tend to be a bit cheaper than the Merc stuff. The cool thing about the Merc props, and I think that they are one of the best for designing go fast props, have an interchangable hub to allow you to run them on all brands of outboards. Cheers, Huey. Link to comment Share on other sites More sharing options...
Little Hooker Posted January 19, 2008 Share Posted January 19, 2008 hey huey, thanks for the prices and info. wow they arent cheap... Is there a market for 2nd ones?? Link to comment Share on other sites More sharing options...
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