85hp, 30mph but sounds & feels like 40, ???

[Dave K.]

Well this has got me. This weekend the speedometer read a little above 30 a wot, but i know this rig & it sounded & felt like mid to high 30's which is average for my 16' 85hp rightly trimmed. now, i was going into the wind & the lake was a bit choppy so i didn't stay at wot for long. it did appear to want to get up to normal wot speed but like i said, i didn't stay wide open for long. any ideas??? i was thinking maybe something clogged in the speedometer intake or cable but i kinda' doubt that. i just hope nothing MAJOR, but like i said, the motor ran great & sounded great, very smooth at low rms & high rms. one last thing, i ran a can of seafoam through two 6 gallon tanks but that wouldn't cause this, would it? i'm a bit stumped!

What do you guys think? thanks dave

 

[paul88]

Re: 85hp, 30mph but sounds & feels like 40, ???

I wouldn't be concerned if your RPMs haven't changed. These speedos are notoriously inaccurate. You're talking about a single sample point on an infinitely complex fluid flow under your boat. Adjusting trim, turning, wake, clogged pickup, can all change what the speedo says, even if your boat speed doesn't change, and the list will never end. Heck, some chipped paint could cause a disturbance on the hull that hits the speedo pickup. The best way to tell how fast you are going is with GPS, averageing your upstream and downstream speeds. Also, one can of seafoam treats 20 gal, not 12, but considering you can put that stuff just about anywhere, its not a big deal.

 

[Dave K.]

Re: 85hp, 30mph but sounds & feels like 40, ???

thanks paul, didn't think it's anything major but always like other's input.

 

[Frank Acampora]

Re: 85hp, 30mph but sounds & feels like 40, ???

Well, if the impact tube is not mounted in the lower leg but is a separate piece that came with the speedometer: Those impact tubes are usually mounted on a spring load of some sort so if you hit anything they will just pop up without damage. The load varies from model to model so if you hit a twig or even some weeds, it may move and the impact hole will no longer be parallel to the water flow. Depending upon how far it has kicked up and original position on the hull, it could read anywhere from full speed to 0 speed.


By the way: Every one (with a medium sized Force or Chrysler) I have ever asked about speed always replies "Oh, about 40." 75 horse on a 19 foot boat--"How fast does she go?" " Oh, about 40." Seems to be a magic number for the smaller outboards.

In the avatar, that is a 90 on a 15 foot hull. It goes "around 40." Actually, 42 GPS with driver and two full 6 gal tanks. With a little playing, I might get it to 45.

 

[Dave K.]

Re: 85hp, 30mph but sounds & feels like 40, ???

Thanks Frank, the lake was a little rough & did some fishing in weedy parts. Not worried. Actually my 16' w/ 85hp does 36-37 properly trimmed. But I have to agree, 40 is the magic speed on the water. in fact just about everyone I talk to who owns a boat says it does around 40. doesn't matter how big, how small, what power - they all do 40...lol, except for the big racing rigs. they do "60 or 80".