Brother and I recently bought a NauticStar Bay 1800 from Florida where it spent all it's life on a lift cruising in no wake zones apparently. When the 2007 Yamaha 115 was serviced before we bought it, it had accumulated 270 hours. 190 of those were below 2000 RPM. We noticed that the boat is quick to get on plane, but when you get the trim settled to make the motor happy the boat wants to porpoise. The tach was not working, but I fixed it yesterday. Come to find out, when the boat is happy and not porpoising, it's turning 62-6300 RPM. The motor seems to sit really high on the boat as well. What's the first step too fixing it? Not sure what prop is currently on it. Was going to drop the motor a little, but 15 years of saltwater has me really nervous of the bolts. I put some kroil on one, and put a breaker bar on it, but I was very nervous when I bowed up on it and it barely moved, and didn't feel right (I've broken my share of bolt heads off). Rather pay someone to tackle that project. All of the testing with the boat has been with a full tank of fuel (36gallons) and just me and my brother (hes about 240 and I'm 185).

First,what is your water pressure at current height? i always run my motors as high as it will go and st have good water pressure. Dropping it will drop your speed and RPM's. Are you running a 3 or 4 blade ? You'll get better performance out of a four blade. Jumps up faster and stays on top at lower rpm's. Won't run as fast as a three,but in rough water, it won't blow out. a three blade will.

Boat does not currently have a water pressure gauge, but I have thought about adding one. The prop is a three blade, and I can figure out pitch when I get home. Currently the motor isn't blowing out or anything, just seems it's having to work a little hard to only be running 33-34.

Either your tach is reading wrong, or your hitting the rev limiter. The rev limiter on that engine will start kicking in at 6100. The boat is bouncing because you have a heavy rig with a lot of weight in it with too small of an engine to keep it strongly up on pad. It doesn’t have enough HP to hold it. Either add a whale tail, or get a bigger engine.

Heavy boat, heavy load, not enough motor. Lowering will probably help a little on the porpoising but it’ll lower your performance on an already underpowered boat. What Is it doing if you run it wide open with the motor only trimmed out about 50%.

Well from what I can discover, the boat is only rated for a 115. The prop is a 16 pitch. . Abolt, that's where it seems to be happiest, but that was when the tach was reading over 6k. Not trying to set speed records, just don't want to stress the engine. One thing is for sure, it is a really efficient motor.
Apparently the NauticStar bay boats are notorious for having porpoising issues, especially in rougher water.

I read your post wrong, I’m sorry. It’s a BAY 1800. I was thinking offshore. A 115 is probably right for that boat, but with weight forward around the center console, the boat is lifting and falling not able to hold itself up effectively. I personally would either add a whale tail, which will help a bunch, or try a 4 blade prop. Maybe also rearrange weight around in the boat.

Short of putting a 150 on it, I would second the whale tail or hydrofoil recommendation. It's a bolt on and if it works and solves the problem, it is a very cheap solution for you. If it doesn't work, just take it off and you're out basically $100 or so. 4 Blade is your other option. You'll lose about 5% on your top end speed but the 4 blade prop will definitely carry the load better and will also bring your rpms down by about 200-300. One other question, are you currently running a stainless or aluminum prop on it?

The prop is a stainless PowerTech NRS3R16PYM. Assume it’s old and discontinued, as google search brings up nothing. From that number I gathered it is a 16” pitch. I was using a flashlight when I looked at it last night and read it wrong. I am not an expert, hence my questions, but that pitch seems a little short?

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwj8n6ySmoLrAhXidN8KHRukAw8QFjAVegQIBBAB&url=http%3A%2F%2Fwww.yamahapropselector.com%2F&usg=AOvVaw2reoJgJIIluQIkcxeUKz35

Yamaha has a propeller selector app. Plug in type of boat, motor specs and it'll give you recommendations. I tried to link to the site but it looks like it failed. Just google yamaha outboard prop selector. Diameter of the prop makes a difference in performance as well as pitch.

Try a mercury spitfire 4 blade. Yamaha props suck because the trailing edge grind is done by hand. Mercury’s trailing edge grind is done by a robot, and it’s the same every single prop that’s done. They are far more consistent from one prop to the next AND are faster than Yamahas props. Plus Yamahas props are probably hard to find right now like their engines. Their stainless props are made in Indy so maybe not but who knows.

I had the same problem. I added trim tabs and I don’t have anymore problems.

Make sure the prop is correct or close at least. Get a shop tach and hook to it and run it - no way it's running 6200 or above as it shuts off at 6100. Boat tachs are notoriously inaccurate.

That prop does not appear to have ever been made. Call or email Powertech and they will get you squared away on the prop. They're really great to deal with. 800-736-7767 (toll free), 318-688-1970 (local) or sales@ptprop.com.

Proptech serial numbers are laser engraved and hard to read especially if used in salt water. If it's regular engraved, it's a prop shop id from a rework and should have 2 numbers in this order - diameter and pitch. The number you listed does not have the diameter listed correctly so you'll have to get that figured out (easy to do - just measure it). Then assume it's a 16 pitch and plug your numbers into a prop calculator to see how close you are.

If all else fails - add a set of smart tabs. They will stop the porpoising. I would be concerned about the tach reading though.

Called powertech, the correct part number is NRS3R16PYM90. 13.25" diameter, 16" pitch. The guy I spoke to was forwarding my information to one of their technicians to call me back and talk about the issue.

I don't doubt the tach is incorrect, but it can't be too far off. This thing is wound up. Got a friend with a shop tach so maybe can get the RPM figured out and calibrate the tach. Thanks for all the info. I know just enough to be dangerous working on outboards.

I'd try a 4-blade but also on some boats, you aren't going to be able to trim up past 50%. I've always just trimmed out until it's running good and running the proper RPM's. In your case, that motor is probably supposed to be in the 5000-6000 RPM range. Sure, you can always go higher than that by getting your prop out of the water. Basically if you can trim it out and hit that RPM range, you are good. Anything else you do from there is to try and get more speed, more hole shot, etc.

edit: just read your post a little closer - you should raise your pitch to lower RPM's. Also, a 4 blade might do the same thing, but you still might need different pitch. 4 blade is for hole shot and not blowing out when trimmed, 3 blade is for more speed. I've owned multiple pathfinder, blazer bays, scouts, a blackjack, etc. Been thru the prop thing with a bunch of them. Never assume the guy that had the boat before you had the right prop on there. Down here on the coast, you can generally find a buddy with a prop to let you try out or a prop shop that will let you try different ones until you find what works. You can also have a prop shop do some tweaks on it to change the pitch a little.

PowerTechs technician called me back. Young lady that flat knew what she was talking about. She recommended first getting the RPMs dialed in to recommend a pitch. But based on the information, the numbers looked like about 20% slip and she recommended a 4 blade in a 14 or 15, depending on WOT RPMs. Said the prop on it has a little more cup making it more like a 17. Said the four blade may slow it down a little, but based on that slip probably not. Can't lose what you never had.

Very impressed with their customer service. If I end up having to order one, just going to give them a call. Seem like good folks to do business with.

Well I think I figured out the tach issue. When I pulled the old Faria gauge, the selector was set to 5P, so I set the new one there. Yamahas have a 12pole, so I need to set to 6p. Going to try to dial it in completely with a meter than can read Hertz.

Good deal - closing in on it.

have your prop checked they can loose the cup, stainless or alum.if you can run close to red line that's good , good cup job will drop 200-400 rpm but will get more left and control

Well as we were getting the boat ready to test the tach, trim went out. It had gotten a little slow on us before but the fluid was low. Figured I'd be having to put seals in it before long. As luck would have it, the manual tilt bleed screw is seized tight, and has been for some time. A previous "mechanic" boogered the slot on the screw head up for me. Nothing for the impact screwdriver to bite. No way to get anything in there to make a new slot. Left hand drill and ease-out time. Oh the joys of owning a boat.

It gets even better. That manual release screw is $149.99 factory Yamaha part. Aftermarket is $75. Just great.