Do boats lose top end speed in the hotter months

[Robertpel9]

I have a 1995 Chris Craft Concept 18 with a Volvo Penta 4.3GS (205Hp).

When i first got the boat in April it would run ~51 on the speedo and a GPS confirmed 48.9

This past 5-6 weeks with the same load with temps consistently in the low to mid 90's I am maxing out at about 46 on the speedo (Have not GPS'ed it) but i have lost 5 mph on the speedo.

Everything is in good running order, looks and sounds great, fluids are good to go

Is this like a high performance car where the engine just likes colder temps or may I have an issue here that is deeper and should be looked into? The air is about 15-20 degrees warmer and the lake i live on (Lake Norman) now has a surface water temp of 85-86 degrees vs about 70 degrees when i got the boat.

Operating temps on the coolant temp gauge are exactly the same all year thus far

 

[gcboat]

Re: Do boats lose top end speed in the hotter months

Yes they do. It all relates to the temp of the air / fuel mixture. Has nothing to do with the temp of the water you are on - but they are both relevant.

 

[jeeperman]

Re: Do boats lose top end speed in the hotter months

All engines theoretically produce more power with cold air intake.

And you might have some growth on the hull creating drag.

 

[marine4003]

Re: Do boats lose top end speed in the hotter months

Around here i lose 5-10 MPH in the dog days of summer due to trying to cut thru 90% humitity.....

 

[Robertpel9]

Re: Do boats lose top end speed in the hotter months

OK good, thanks for the replies, i feel better now.

I jusp in every weekend with a brush and wipe down the outdrive and the entire hull to get off any growth before it gets a chance to stick and i am about 90% successful so i do not think i have extra drag but today for instance it is 97 and humid so i am slow

 

[oops!]

Re: Do boats lose top end speed in the hotter months

i will abosluetly gaurentee you that unless you lift your anchor, or untie the dock line your are going to go slower reguardless of outside temp....

all funnin aside,

in a hot day, air is expanded, not as much in the cylinders. less heat generated, less bang in the holes.

on a hot day an airplane will require longer runways than normal beacause the air is "thinner".

take the boat out on a cool morning and see what happens.

just make sure to lift that anchor !

cheers
oops

 

[stevewolverton]

Re: Do boats lose top end speed in the hotter months

Around here i lose 5-10 MPH in the dog days of summer due to trying to cut thru 90% humitity.....

Up to 10mph!?