New Boat GOOD!

FlyingV5

 
4.2 hrs. on the meter, the FD196OB (115HP Yamaha 4-stroke) runs 41&1/2 mph with the top up or down. Revs want to go past 6000 so I have to throttle back. Anybody know what sort of prop would load it down to about 5800rpm? I bet it will do 45mph with more propellor. This is a sweet boat, it gets up on plane and jumps wakes like a jet ski. Not one drop of water splashed onboard yet. And it turns at full speed like a zero-radius lawn mower. I am going to have a lot of fun with this boat.

thurricane

Standard prop for a Yamaha F115 would be 13.25  x  17 pitch alum.  If you want further specs you could go to the Yamaha website under performance data.

thurricane

Standard prop for a Yamaha F115 would be 13.25  x  17 pitch alum.  If you want further specs you could go to the Yamaha website under performance data.

FlyingV5

My prop is 13 X 17 K. So it is a bit smaller than what you quote as standard, tgipsonhurricane. That makes sense because I can give it full throttle on smooth water, and just about the time I get it trimmed right the revs hit 6000, so I have to pull back. I feel like I could add maybe 10% more prop. I want it to not quite be able to reach 6000 rpm at WOT and I think that would be at least good for 45mph.  I have read testimonials about 4-blade props. I want to go SS and because that is expensive I want to get the right prop the first time. Any advice is welcome.

Ernest_T

Going to a 4 blade prop tends to give you more hole shot and reduce planning speed, but you usually loose some top end speed. For example, I went from a 3 blade 17 pitch SS Yamaha prop on my F150 to a 4 blade 15 pitch SS PowerTech prop. My goal was different than yours, I was trying to increase hole shot, and reduce planning speed. My max. rpms dropped from 6000 to 5800, and I lost about 2 mph in top end speed, but I did achieve my primary goals. In your case if your goal is more top end speed, I would recommend staying with a 3 blade prop, and try increasing the pitch. I'd say a 19 pitch prop would probably put you right where you need to be. I would highly recommend the PowerTech props. I contacted them, told them my setup and my goals and they recommended a prop (actually they gave me 2 choices). Their props are not cheap, but are very nice, and the guy I spoke to was very helpful. Whatever you try, I recommend making sure that you can return the prop if it doesn't work out. Finding the correct prop is somewhat of a crap shoot to get it dialed in exactly.

FlyingV5

Ernest T, your comments interest me. I have already noticed that this boat needs quite a lot of speed to get on plane, then I can back off just a bit but not too much and keep it there. Thinking that if I am towing a tuber, the minimum speed may be too much for some riders. How does your 4-blade prop do in that regard? Did you get on plane quicker? I might be willing to give up some top speed, particularly if the boat could then be piloted by others with no worries about over-revving. And then I have been warned that a SS prop will transmit damaging shock loads to the delicate transmission parts in case of striking something, while aluminum will bend or break. But my prop has a rubber core, so WTF? After I have a bit more time on the boat I may just talk to your PowerTech boys. 

Ernest_T

What I found with my boat with the original setup and prop, was that planing speed was around 19 mph. My son and daughter wakeboard, and they preferred speeds around 17-19 mph. This made it very difficult to pull them, because I was constantly falling on or off plane and manitaining a constant speed was nearly impossible. The other problem was that they wanted to be popped up quickly, and my hole shot was not great with the original 3 blade prop. My first addition upon the advise of a couple of other Hurricane owners on another forum, was to add trim tabs to my boat. I installed the Smart Tab system, which is an inexpensive automatic trim tab system seen in this photo: [link=http://ernest-t.smugmug.com/Family/Boating/i-x4rBM3Q/0/L/Trim-Tabs002-L.jpg]http://ernest-t.smugmug.c...0/L/Trim-Tabs002-L.jpg[/link] The Smart Tabs were an excellent addition to the boat. My planning speed dropped from around 19 mph to around 16 mph, which made it much easier to maintain a good wakeboard speed for my kids. The system was easy to install, and had additional benefits of reducing the bow rise and smoothing the ride in choppy water. I highly recommend them. Initially, I noticed a small decrease in the top end speed with the Smart Tabs, but that was because I didn't have them adjusted properly. After contacting the company, and adjusting them correctly, there was no loss in speed. I still lacked the hole shot I wanted, so that is when I contacted PowerTech and got my 4 blade prop. The 4 blade prop improved hole shot, with a small loss in maximum speed, and the combination of the Smart Tabs and the 4 blade prop reduced my planning speed another couple of mph to around 14 mph, which was great for my kids wakeboarding. Now that I have everything dialed in, I'm running about 2 mph slower than the original maximum top speed, but that doesn't matter to me (my wife seldom lets me go fast anyhow). What I've gained is that the boat pops up on plane much more quickly and maintains that speed at nearly 5 mph slower speeds than with the original setup. I also get the added benefits of less bow rise, and a smoother ride thanks to the Smart Tabs. The PowerTech people claimed that this setup would also make the engine run more fuel efficient, but I have no way to really measure that.

Ernest_T

The other thing about the PowerTech prop was that it came with what they call a "Cushion Lock" hub system. This system protects the engine if the prop hits something in the water, and also reduces the "Clunk" sound you hear when shifting.

FlyingV5

OK, I have to tell about the test. The guys at the factory know something after all. The stock prop (13.25 x 17K) is just about right. Over the Fourth of July holiday I had opportunity to operate the boat with a full load several times (maybe just a little over weight with three sisters in law). What I found was that on smooth water the boat will run about 38mph @ 5800rpm full throttle. This is perfect as far as loading the motor, but I don't understand why the revs drop with more weight. I would have guessed that since the prop is already submerged and not sucking air, it would have slipped just as much as with a light load and run the same revs but at a slower speed. I would have been wrong. Can anyone explain to me in engineering terms why the revs drop with more hull in the water but the same prop? By the way, everyone agreed the boat is great. 

Ernest_T

I had to tow a disabled boat last weekend. I noticed that my max rpms were around 3500 at WOT instead of the usual 5800 (top speed around 9 mph). I actually towed slower than that, but pushed the throttle up on a calm stretch just to see how fast I could go, so an extra load definitely has an effect. I can't explain it in terms of engineering, but my guess is that the prop speed depends in part on the speed that water passes through and around it. With an increased load the water stacks up around the prop rather than passing through it (remember water is not compressible), so the prop is exposed to more and more resistance to rotation as the load increases. This increasing load on the prop is transferred to the engine and therefore the rpms drop.