Yamaha 4S 115 Overpropped?

[Gary Tuthill]

Hello: I recently purchased a 2004 Yamaha 115 four stroke mounted on a 2003 Lund Pro Sport 1700. The boat is an aluminum dual console which weighs approximately 1000lbs. Initially during breakin I used Yamaha's black 13x19" stainless steel prop but could get no better than 5300rpm's at wot. Now, I switched to the stainless and vented 13 1/4x19" prop and get 5000-5200rpm at wot. Hole shot seems better but still not what I had anticipated. Clearly this needs to be reduced to a 17" prop (on order by the dealer) but I have concerns over this. I've searched here and all over the internet and it seems that on similar boats this motor has predominantly 19" props and occasionally 21" as well. While a 17" may get it to the desired rpm level I wonder is there is a problem with the boat or more to the point, the motor itself? With five adults, all near sitting behind the windscreens, I had to run to the bow to get it onto plane. I'm feeling that at any given speed, the 17" will add noise and reduce fuel economy.<br /><br />Next question is how do I measure wot rpm's? Is it one person in the boat, and motor trimmed as far up as I can without getting too much cavitation?<br /><br />Thanks to all. gary tuthill

 

[spete]

Re: Yamaha 4S 115 Overpropped?

consider that 5 people will create a load of possibly 700 to over 1000 lbs additional weight and then you've got gear, ice, tackle, etc. to add to that. Your top end problem is most likely a weight issue. Not positive but WOT operating range is typically 4500-5500 and you're right there at 5200. The 17 should give you the hole shot you're looking for but you'll sacrifice top end speed. Try loading heavy gear, coolers, etc. towards the bow and put the bigger people up front if possible. If this is a 17' aluminum boat 5 people may be streaching the limits anyway. How does it run with just you or one other person? Sounds to me like you're possibly just overloading the boat beyond what it's really capable of handling. Good luck!

 

[Dhadley]

Re: Yamaha 4S 115 Overpropped?

When you say the other boats you read about were the same, were they 4 strokes as well?<br /><br />A set up with too low an X dimension will do the same thing as you describe. Try raising the motor on the transom.<br /><br />Good luck!

 

[spete]

Re: Yamaha 4S 115 Overpropped?

dhadley - if he's having trouble getting the boat to plane won't raising the x dimension worsen the problem? I thought you'd want more foot in the water, not less? Is it possible that this aluminum boat wasn't designed to have the heavier 4-stroke motor?

 

[bossee]

Re: Yamaha 4S 115 Overpropped?

Hello: I recently purchased a 2004 Yamaha 115 four stroke mounted on a 2003 Lund Pro Sport 1700. The boat is an aluminum dual console which weighs approximately 1000lbs. <br />------------<br />Hi,<br />Is 2004 Yamaha F115 already out...? I just bought a new F115 2003.<br /><br />I checked out how a Lund Pro Sport 1700 is on a picture. Nice boat!<br /><br />-------------<br />Initially during breakin I used Yamaha's black 13x19" stainless steel prop but could get no better than 5300rpm's at wot. <br />-------------<br /><br />5500 rpm gives max output on this outboard but recommended rpm range is 5000-6000 rpm as You can see in Your F115 Manual, specifications.<br /><br />-------------<br />Now, I switched to the stainless and vented 13 1/4x19" prop and get 5000-5200rpm at wot. <br />-------------<br /><br />Larger diameter will increase drag and do not perform as good as lower diameter prop at high speed. It is pitch you should change, really. As a rule of thumb a 1 inch change in pitch rase or lower the rpm by 200 rpm. So if you had Yamaha 13x19 SS prop and 5300 rpm, change to 13x17 SS Your rpm will be around 5700 rmp.<br /><br />------------<br />Hole shot seems better but still not what I had anticipated. Clearly this needs to be reduced to a 17" prop (on order by the dealer) but I have concerns over this. <br />------------<br /><br />Your top rpm will probably be OK with a 13x17 prop since you probably will get 5700 rpm or around that and is well withing specification: max 6000 rpm.<br /><br />-------------<br />I've searched here and all over the internet and it seems that on similar boats this motor has predominantly 19" props and occasionally 21" as well. <br />-------------<br /><br />13x19 is "standard" prop on the F115 unless you have special needs, 13x21 will mean little higher top speed (1-2 knots) but slower acceleration. 13x17 could also be an alternative, like in your case.<br /><br />----------<br />While a 17" may get it to the desired rpm level I wonder is there is a problem with the boat or more to the point, the motor itself? <br />---------<br /><br />Probably nothing wrong with your boat and outboard.<br />Your outboard seems to have rpm enough with the props you have tried so far and a 13x17 will get a good top rpm of 5700 rpm.<br /><br />-------------<br />With five adults, all near sitting behind the windscreens, I had to run to the bow to get it onto plane. I'm feeling that at any given speed, the 17" will add noise and reduce fuel economy.<br />--------------<br /><br />As said by another person in this thread, move some cargo to the front. Heavier people more forward. And remember 5 adults is heavy load on this (after all rather) small boat. You should make judgments about normal acceleration and top speed comparisons with 2 persons generally, I think. <br />When I see the specifications for Lund Pro Sport 1700:<br />Length: 17 ft. 2 in. / 5.23 m <br />Beam: 7 ft. 0 in. / 2.13 m <br />Weight: 1,056 lbs. / 480 kg <br /><br />This is considered a rather small boat, at least with 5 persons on board, and you have also a 115 hp outboard hanging on it (over 400 lbs!).<br /><br />Before you accelerate, use the trim to get the rigg trimmed down close to stern and this way keep the nose down while acceleration to plane. When in plane you trim out the rigg until the the boat has a nice angel of attack to the water (see the trim meter on your Yamaha LCD guage and use trim on the gear handle so the vertical bar shows about in the middle).<br /><br />More rpm will generally increase noise.<br />Fuel economy: maybe a little more fuel at top speed, but nothing to worry about I would say. You need to find some tests with our boat and outboard combination including prop same as you to tell for sure what is going to happen. There is a LCD Yamaha Fuel Management gauge for those interested to "know" about fuel consumtion:<br /> http://www.yamaha-motor.com/accessories/otb/helm05.html <br /><br />------------<br />Next question is how do I measure wot rpm's? Is it one person in the boat, and motor trimmed as far up as I can without getting too much cavitation?<br />------------<br /><br />Usually 1-2 persons. Trim so the trim guage has the vertical bar about in the middle. You will also feel and hear when the boat+engine is going optimal because if right trim.<br /><br />My personal conclusion about your boat and the F115:<br />Since the boat is not so large and 5 persons load seems to be when trouble starts I would say it is almost normal behaivior. This small boat can not do "magic". I think you will have to live with some acceleration problems when 5 persons are on board, but consider loading the boat smarter and use the trim wise. Hopefully the 13x17 prop will give better acceleration and it will give better top rpm (close to 5700 rpm). But still, 5 persons is rather much load on this boat considering the specifications for the boat.<br /><br />/Bo

 

[Gary Tuthill]

Re: Yamaha 4S 115 Overpropped?

I'll clarify a couple of things but it looks like I just need to get the Yamaha 17" black stainless prop.<br /><br />I assume Lund has taken into consideration the installation of heavier four strokes. In fact, the boat came prerigged for Yamaha.<br /><br />I had trouble getting on plane when there was nothing of weight in the front of the boat. Actually, the only weight was fuel and people, all in the back half. If the rig is slightly overpropped, then difficulty in getting on plane under these conditions is understandable. While rated for seven people, I realize this doesn't mean they can necessarily all be in the back end. In addition, I nearly always start on the lowest trim setting and then go up after on plane.<br /><br />I assume by "x dimension" you mean the x axis, or verticle height of the motor. I'm going to check this on Monday when I'm off call here at the hospital. That may be a way (raising the mounting height) to raise wot rpm's without going to a smaller pitched prop. The poor holeshot under certain conditions is something I can easily live with. That may be a better first try than a prop change. On the other hand, the boat does tend to cavitate (blow out?) on relatively easy turns, even when trimmed all the way down. Agian, this is probably normal, just not what I've experienced in the past with fiberglass runabouts.<br /><br />As for the year of the motor, it is in fact a 2004. I did not get it until some time in June. I doubt there a any changes with the 2003.<br /><br />Essentially, I need to either reduce the pitch or raise the motor to get closer to the ideal 5500 rpm at wot. <br /><br />Thanks everyone for their input, this board has been most informative for me. <br />Gary Tuthill<br />Britt, MN