Tri-hull 55hp Prop size help please

[budbecks]

Hi,<br /><br />I will explain to use as best i can the setup and description so that someone could possible help me determine my best usable prop size.<br /><br />Engine - Yamaha 55hp 2-stroke electric start 1984/5 model 100:1mix<br />Prop In Use - OEM 48-73134-a40-12p ( which i think is a 10.5" x 12" made for mercury engines)<br />Max RPM - Unknown - See below<br />Hull Design - GRP Tri-hull or Cathedral Hull<br />Jackplate - None Used<br />Foils - None Used<br />Intentions - Mainly fishing but would like to get around fast.<br /><br />Ok, i brought the boat last year and we had a good years fishing on it. However, the boat drank fuel like there was no tomorrow ! We had the engine serviced end of last year and guy said that we have the wrong prop fitted. Not surprising that when i looked up the number on the prop (48-73134-a40-12p) it turn out to be a oem number for a mercury prop, yet the engine is a yamaha. I have 2 other props which i have brought of ebay which are (11.75 x 12)<br />(10.75 x 17). I have put both the props on and the larger prop 11.75 is the largest prop that will fit diameter wise. There was no rev counter fitted to the boat but i have now got a rev counter and will be fitted for the new season. I would like the best suitable prop for speed mainly as we use it to get between fishing spots.<br /><br />More info:<br />Holds between 3-4 persons average.<br />Holds minimal fishing gear, 2 x 24ltr tanks<br />Cant weigh the boat at all as trailer is no good and waiting for new one and even then have no where local to weigh.<br />A picture of the boat can be found here:-<br /> http://www.dvddealsuk.co.uk/boat <br /><br />Thanks for any help anyone can give. I will give you any more info you require just ask.<br /><br />thanks again<br />John

 

[rickdb1boat]

Re: Tri-hull 55hp Prop size help please

Hi John,<br /><br />The best prop for your boat will be a Stainless one that will allow you to reach the top end of your RPM band. Without knowing your Max. RPM's now, there is no way to tell what pitch prop you need. Install the Tach. and let us know what RPM's you are running wide open and we can go from there.

 

[Silvertip]

Re: Tri-hull 55hp Prop size help please

Your WOT RPM test should be made with what you consider a normal load. If you fish alone most of the time, then make your test runs with just you in the boat. If you normally fish or cruise with two or three in the boat, then make your test runs with that load. A prop selection for normal load (such as two or three people) will allow best performance loaded but may exceed the high end of the RPM band by a couple hundred RPM. This is not bad and besides, you can throttle back a little if necessary. But if you prop for one person, you will lug the engine with a heavier load and that definitely is not good.

 

[budbecks]

Re: Tri-hull 55hp Prop size help please

Thanks for your replies and help.<br /><br />A few more things to tell you that i forgot.<br /><br />The prop i have taken of is a mercury prop or made for a mercury and this prop is now unusable (broken). However the yamaha props i have brought from ebay said yamaha props and all yamaha props seem to be white which is what i have. The reason im telling you this is the 2 new props i have have a smaller stock than the mercury prop so when i install them on the prop shaft and do the nut up, theres is a 1/2 inch play so the prop is not on the staft properly. The splines are right but not the stock.<br /><br />Can i put some washers on just to hold and test a prop ? Else whys i am going to have to buy a prop to test. (if you see what i mean) Probably a mercury prop too.<br /><br />My engine runs fine but is cosmectically in a sorry state and is currently being full resprayed.<br /><br />I will be installing the Rev counter and as long as i have A prop to test then i can give you a rpm reading.<br /><br />I dont know if this will help but when we had the engine on there before we could only ever get up to about 75% WOT and anything over that would just sound groggy and the boat would vibrate. We never really took the engine over this mark as the fuel was gone in a flash and it couldn't of done the engine any good.<br /><br />thanks again.<br /><br />John