Why is my boat slowing down??
 

Just curious. My boat seems to be losing mph. All variables being the very similiar- give or take a gallon of fuel or a degree in air temp. I seem to have lost about 5 mph! Any suggestions?

Re: Why is my boat slowing down??
 

You tend to lose MPH as the summer starts to lose the cool air. Just by chance, are you leaving your boat in the water. It's amazing how fast a film and then growth will attach to the bottom which in turn causes the speed to slow. Assuming your boat appears to be running ok.
VeeCat

Re: Why is my boat slowing down??
 

Give us some more info to work with. Over what kind of timeframe and/or events has this slowing occurred? What boat and motor(s) do you have? How is it stored? What were the water conditions during each run? Tab/Drive positions?

You could have any number of things going on, each of which are alluded to above, but this is by no means an all-inclusive list. We've seen everything from limp-mode on EFI motors, bad gas, and believe it or not, your boat probably will not give the maximum speed on glassy calm water. You need a foot of chop or so to help aerate the bottom. Wind conditions, humiditity and atmospheric condiitons, as well as river or tidal currents also play a role. Some days you just don't have it, and fumble with trying to get the boat trimmed out and run stable...

Re: Why is my boat slowing down??
 

Are you loosing rpms also?????

Re: Why is my boat slowing down??
 

1)Take all of the crap out of your boat then see what you really need in there.

2) Are you taking on water? Maybe your auto bilge pump is not pumping out at the same level. You may have more water in your bilge than when the switch was working correctly.

3) Is the bottm clean? That for sure will do it but that is just way too obvious, right?

4) Have you or the people you socialize with gained weight over the winter? :D

Re: Why is my boat slowing down??
 

Once our little SBC powered Baja 196 Sunsport was losing speed little by little and we were scratching our heads. It was summer and we finally just decided the warmer humid air is just killing the power. Finally one day the motor just quit while running WOT. Got a short tow to the dock and started checking things out and found the distributor gear was worn paper thin and finally failed completely. As the gear wore the timing became extremely retarded. We marked the distributor and intake manifold and it never moved, so we never checked it. Put the new gear on and the speed and power returned!!! :drink:

Re: Why is my boat slowing down??
 

Craig, why did the distributor gear fail? Was it just a brass gear?

Re: Why is my boat slowing down??
 

Dan,
No clue why the gear failed. At the time the motor had a flat tappet solid lifter cam. When we rebuilt the motor the cam gear looked fine. With the flat tappet cam we ran a steel gear. We replaced the distributor gear with another steel gear and after 2 seasons of running it looked fine. Only thing we can imagine is the distributor gear that failed had some hardness issue or something similar.

Craig

Re: Why is my boat slowing down??
 

More Info:
Boat: Baja 29 Outlaw 2002 w/496 mag (375 h.p.)
Hours: 130
Complete Service every 30 hrs. Oil, Drive, Check fill all fluids, check Air Filters.
Water Pump pressure at 3000 rpms - 14lbs.
No signs of elavated (according to computer scanner) Oil temp, Water Temp. Furthermore - Every other warning code has come up clear, or within the specified margins.
Oil Pressure Good - Oil used is Mercury with Mercury Oil Filters

Water Conditions -
Last season the boat would run at 4850 RPMs with a Approx 1/2 tank of fuel a consistant 70 - 73 mph (Depending on chop, and wind direction, with waves or against)
This year - Same RPM, Same Fuel Load, Same water Conditions, Approx Same air temp (give or take two degrees), Same Location, Same equipment in the vessel. - 67-68.
Speeds are obtained by GPS.
Boat is stored on Trailer inside a Portable Cover-it tent.
Currently I am running a set of 25p Mirage Plus 3 blades that have been turned to a 27p cut to a 14.5 diameter. The props were finished by Mercury racing (the Late Dennis C. Himself) and were sent back to perfect their performance 3 times. When I recieved the props I gained a consistant 3.8 mph (GPS)
Props show no signs of dings or dents, nicks or scratches.
At this point I would like to gain what I have lost.
I have heard rumors that the bottom may have been affected from sitting on the trailer.
If you need more info let me know.

Re: Why is my boat slowing down??
 

If you are not happy with all of the abvoe check the distributor module. It will rob you of 5-8 MPH.

Re: Why is my boat slowing down??
 

I recently burnt out a distributer module/rev limiter (HP 500)
and seemed to lost 300 RPM/ 5 MPH after I replaced it, I'm baffled, Going to try DUI distributors this weekend & hopefully recoup my lost RPM's.

Re: Why is my boat slowing down??
 

Hazy, Hot and humid his summer. Last summer in CNY was cool and windy. The lakes have been glass and the air is hot and humid. I've seen similar results this year, loss of speed and no changes. Like anything else in CNY, blame the weather :drink:

Re: Why is my boat slowing down??
 

If you read Need-the-speed's last post, he says same RPM's. Everything else being the same (which he says it is), it looks to me like his prop slip went up (less speed + same rpm= more slip). The big question now is why??? Most of the posts (except Griff) are assuming a loss of rpm. Need-the-speed, Did you add anything to the boat that could disturb water flow? Like a new depth transducer?? You'd be surprised what could cost you speed. Especially when you have everything tweaked. I had a 17' speed boat that after a lot of tweaking did 72mph. Then one day I added a depth finder. I took the boat out and found I lost 4-5mph! (Radar). I removed the transducer right in the middle of LI sound (Quick release transom mount). I got my 5mph back right away. From that day forward, I learned the value of water flow along the hull:)

Re: Why is my boat slowing down??
 

I'm absolutely stumped. I have not added any typ of device to the hull of this boat. This is really driving me nuts! Maybe I'll try my other props for kicks. :(

Re: Why is my boat slowing down??
 

If the rpms are the same, I would lean toward a hook having developed.

Re: Why is my boat slowing down??
 

Thinking about it now, when my boat lost speed, it also lost rpm (Prop slip remained virtually the same).
Griff, a hook could slow it down, but I would think you'd see a corresponding decrease in rpm's, and probably a difference in boat attitude. Need-the-Speed, are you sure the rpm's are the same?

Re: Why is my boat slowing down??
 

Possibly, but not necessarily. If the engine is making its power, the hook will just make the boat ride wetter and with more prop slip.

5mph is still a ton to loose.

Re: Why is my boat slowing down??
 

Would a drive shower sticking down an inch cause any speed loss?It's right inline with the edge of the prop. It's one of those single side showers.

Re: Why is my boat slowing down??
 

:( take a 6ft. strate eadge , check the bottem for hook, thats a space under the center of your strate edge ,, or if you have a rocker, as the word implies :evilb: fountain says 1/16in. space,. hook is worth 10 mph :eek: :eek:

Re: Why is my boat slowing down??
 

Holy $hit 10mph!!!! I may have the bottom checked. Perhaps a good Blue printing is in order. Thats going to cost :( Maybe I'll just save the money and drink my sarrows away :rolleyes: