Hi everyone - hope everyone is enjoying the season.

Has anyone experienced lower speeds since the temperature has warmed? I'm in southern Michigan and the temps have been in the mid 80'sF. Earlier in the spring when it was rather cool - 60F I could easily hit 63-65 mph. Now with the warmer temps I'm at a struggle to hit 60. Engine is running wonderful- bottom of the boat is clean - no dings in the prop. The only variables have been what I call a tank of jip joint gas - (Admiral) and the warmer temperatures. I've since refueled with Shell (89 octane) but no increase to what I experienced in the spring.

Thoughts?

Safe Boating!

3pointstar

Cool air is more dense than hot air. More air, more fuel, more power.

I notice 3 to 4 mph loss when going up 3000' in elevation. Very slow out of the hole.

You will certainly see a decrease in speed as it warms up. The hotter it gets, the slower it gets because the less power it will make. Hot air is less dense than cooler air. Therefore, the engine will take in less air (oxygen) with each stroke.
Eddie

yes sir you are correct. warm air and humidity decrease engine performance. it also decreases lift on an aircraft in the same manor.

Yup! My boat runs like a scalded ape in cool weather. A couple weeks ago, I was getting 5100+ RPMs. In hot weather I barely get 5000.

hey, we could all go out to the sand bar in January. stand around in knee-deep water drinking beer and talking about how fast our boats are...

Running late October dry air and 50 degrees is a lot different than 80+ with humidity. Also last run I am low on fuel and gear. It is noticable.

Seems to me I remember 1% increase in H.P. for every 10º drop in temp.
Technical article stated 1.9% for 20º drop so I was close.

It always kills me on how well the boat runs in late fall just before I put it away for the winter.