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I just bought a 1987 Striper 15. It is rigged with a 1999 Yamaha 4 stroke T50TRLX. The current prop is an AL 13.5 X 16 (chewed up). I have run it up to 5200-5300 RPM, WOT, however, I was not fully trimmed out and it was running about 32-34 MPH. The factory manual shows the RPM range from 5000-6000 WOT. The boat seems to like to cruise around 4200 RPM at 24 MPH. I would think I should be able to cruise that same speed at 3700-3800 RPM. If anybody with the same boat and similar HP could let me know their Prop Size and what RPM and speed they are getting it would give me some baselines. Props are too expensive to guess! The "T" in my Engine Model stands for High Thrust if that helps at all. Thanks in advance, Forrest
I owned the same model in the 70's , 55 Johnson w/ 13 sst prop, and ran in the low to mid 30's wot.
Check out this link for more info on props http://www.marksmarineinc.com/prop_calc.aspx
Yes, it is very important to note that you have a Hi-Thrust model as the gearcase and gear ratio are completely different than a standard Yamaha 50.
The Yamaha T50 uses an intermediate size gearcase with a 2.33:1 gear ratio. We know a Striper 15 with 50 HP should be good for 35-36 MPH.
If by "AL" you mean you have an aluminum prop, I am not sure what it is. Yamaha does not make any aluminum props for the intermediate gearcase motors with 16" of pitch. They do make a 13-1/2" x 15" and 13-1/2" x 17" aluminum propellers.
They also make a 13-1/2" x 16" Painted Stainless Steel propeller model.
If you are getting 33 MPH at 5250 RPM then that's about 3 percent slip which is very low for a "chewed up" prop and makes me suspicious.
At any rate, what propeller you have now is not as significant as what propeller you should have. At WOT you should be close to 6000 RPM lightly loaded. I suggest you switch to the 13-1/4" x 14" Yamaha Performance Series 3-Blade and make sure the motor is mounted two or three holes up on the transom.
I have a 13.25 x 13 Stiletto Advantage that should fit your motor. I bought it as a ski / tubing prop for my Supersport 15 / F70 combination, but in fact the 15 pitch works just fine.
You are welcome to borrow my prop for a test (you pay shipping) or I'd also be interested in selling it. Please contact me via PM or at address in profile if you are interested.
I have had some carb issues with the new boat, I just got it back going this past weekend, I am going to take it out on calm water with a hand held GPS and see exactly what it will do, I have been afraid to run it real hard with all the issues I've had. I will have my son write down the data and report back my findings, I used a Sea Tow Ap on my phone for the MPH readings, the Tach reading are accurate. I guess the motor will have a Rev Limiter on it, I am told to trim it up until it slips, and then go back down a touch...The motor is 1.5 inches above the transom, so I believe it to be correct.
Thanks for your help, Please respond agin in a couple of days once I report more accurate info,
Regards,
Forrest
I think the 13.25x13 Stiletto would be very good to try. I don't know how chewed up your current prop is, but you're certainly losing some effieciency there, and of course aluminum is less efficient anyway. The Stilettos seem to have a much higher effective pitch than the nominal, so the 13-pitch may not be all that much of a change from your current prop. But if you're working OK with a beat-up aluminum prop right now, you'll be able to move the motor up at least one hole on the transom when you put the Stiletto on. I'd guess the Stiletto may give you, on net, 2-300 RPM over your current prop, and moving the motor up possibly another 1-200, which will put you right up at the top of the RPM range where you want to be.
In your initial post, you talked about wanting to get to a lower cruise RPM. "Cruise" is something of an ambiguous term - the motor testers define it as the planing speed at which you get the best mileage, but I'd guess you're using it more generally, to mean a comfortable speed, solidly on a plane but not working the motor too hard. With your T50, you may well find that 4200 RPM / 24 MPH is that comfortable speed - my F70 settles in nicely at about 3700 RPM / 24 MPH / 10 mpg which would seem to correspond to your experience.
So, I bought the 13.25x13 Stiletto from Tim, I couldn't be more pleased, I increased my RPMs by about 150 RPM and my speed increased to 34.6 MPH, it jumps out of the hole a lot better and by comfortable cruising RPM is a bit lower at a higher speed. however, I'm still only getting 5450 RPMs out of the motor. Oh, all testing was done with both my boys, and I in the boat, about 450 lbs and 12 gallons of gas, so, I still believe lightly loaded it would go a bit faster.
I have a couple of questions about how the boat reacts...when I jump it on plane, with the motor trimmed all the down, the boat pulls hard to the right, as I trim the boat up, I feel the boat lift out of the water and I am able to let go of the steering wheel and the boat steers straight...Now, if I go for more trim, I feel the boat really lift out of the water and I feel like it's only riding on a couple of inches of the stern, the boat then pulls really hard to the left, to be honest, it's not a speed i would ride at for long peroids of time, but, if I were to be caught in a squall and need to get back to the dock, I would utlize all the power the motor had to offer...The enginge bracket is 1.375 inches above the transom, but the motor mounts are in the top holes, however the bottom bolts are not in the slots, they are thru bolted in the bottom holes, thus to me, moving the motor would require some plugging...Any thoughts? Thanks for all the input you guys have offered.
Regards,
Forrest
Forrest, glad it's an improvement - going from 5400/31.6MPH to 5550/34.6MPH is not too shabby. I think your pulling issues may have to do with the mounting height. It's hard to tell your transom setup from the description - do you have a pic you can post on your personal page? And a key measurement is the vertical distance from the keel line to the antiventilation plate, with the motor trimmed so the plate is parallel to the keel. As mentioned above, going to the Stiletto should allow you to move up at least one hole from what worked well with the old aluminum.
The propeller torque you feel through the steering system is perfectly normal. It will be GREATLY reduced by raising the motor on the transom.
If the auxilliary bolt hole locations were used for the lower bolts, those holes need to be filled in the transom and new holes drilled on the BIA lateral spacing. This is a very easy chore once the motor is off the transom.
Forrest, after re-reading your post, it sounds like maybe your motor was mounted using the upper and lower pair of mount holes in the bracket, and the lower slot was not used at all? If that's the case, I can guarantee you your motor is mounted way, way too low. I have seen people mount motors this way on 15s before, and in my opinion it's really lame - just not mechanically sound. And as you have found, performance is suboptimal.
The good news is that you can fix this pretty easily, although you will need a chain host or the ever-popular "rope over the shade tree" method to get the motor off the transom. Assuming your upper holes are positioned as per the diagram here http://www.whalercentral.com/articles...icle_id=82, that is, 1 7/8" down from the top of the transom, then all you'll need to do is remove the lower bolts and fill the holes, then install the motor again using just the top bolts, but in hole #3, counting down from the top 1 2 3 4. You can then re-drill the lower holes at the top of the slot - you may or may not find you need a slight up angle to get into the splashwell, but most likely you will not. I know that your new prop will work well in that configuration (because I have tried it) and if you find later that you want to try it one more hole up (#4) then you'll be able to do so without redrilling.
I think you'll gain another 100+ RPM and probably about 1 MPH, but it's the handling improvement you'll notice most.
You are exactly correct on how the engine is currently mounted on the boat and the digram is correct for my configuration. Would wood dowels cut 1/2" short and then feather filled on each side, be fine for repairing the old holes?
I am going to do this. I fear my 16 year old may borrow my boat when his 13' Whaler willl not accommodate he and his friends, my biggest fear is accidentally letting go of the wheel and throwing somebody out. I did this 25 years ago in a 13' Whaler with a tiller engine. (some how the guy didn't even spill his beverage)
I think you may be able to find some articles on filling transom holes by searching; I have not done the job myself so don't want to steer you wrong. Your choice of solution will probably be dictated more by how cosmetically perfect you'd like it to be than by any structural concern - there are plenty of ways to make it waterproof.
You'll be pleased with the results - less bow lift on takeoff, more speed, improved mileage, shallower draft, lighter steering.
Do not use dowels to fill the holes, use wood plugs. I epoxy them in and the 'glass over the ends of them and top off with gel coat patch paste.
You can also just fill them with polyurethane caulk, but it doesn't look as nice.
You can eliminate any steering feedback by switching your steering system to a No-Feedback (NF type from Teleflex. A complete kit is less than $200 and is very easy to install. I recommend the Safe-T-II NFB which is exactly like what you have except that when you let go the wheel, the NFB feature prevents it from moving.
You can also buy the NFB 4.2 which is simply a geared down version so the wheel is easier to turn, but you have to turn the wheel more to achieve the same alteration in course.
type from Teleflex. A complete kit is less than $200 and is very easy to install. I recommend the Safe-T-II NFB which is exactly like what you have except that when you let go the wheel, the NFB feature prevents it from moving.
