Boat Speedo

Our technical section for all matters related to the care, maintenance and restoration of your classic boat.

Moderators: Alacrity, Rapier

Post Reply
kwoffa
Posts: 120
Joined: Wed Nov 01, 2017 1:09 pm
CMBA Member: 1180
Location: surrey

Boat Speedo

Post by kwoffa »

Hi Chaps,
I have just bought a classic speedo for my boat,however i have no idea about these things,it is not electricly powered,and does have a long tube coming out of the back,my questions are,What goes on this tube? and how does it work,i am really pleased with this unit..as it is from the same era as my boat,,anyhelp would be apreciated...TIA.Mel.

User avatar
floater
Posts: 1065
Joined: Fri Feb 06, 2009 6:47 pm
CMBA Member: 90
Location: Southern England

Re: Boat Speedo

Post by floater »

You have a pitot type speedometer, inside its a bit like a barometer working in the same way. The tube needs to be connected to a pickup on the back of the boat. The speedo responds to the pressure of the water rushing past the pickup. You can simulate the water pressure by blowing down the tube but you'll be surprised how much pressure is needed to move the needle. I checked mine using a conical adapter on a foot pump

See the lower half of this page:-
https://www.jamestowndistributors.com/u ... ?docId=836

Pickups are readily available from most chandlers.

kwoffa
Posts: 120
Joined: Wed Nov 01, 2017 1:09 pm
CMBA Member: 1180
Location: surrey

Re: Boat Speedo

Post by kwoffa »

Thanks a lot,,, thats what i thought i needed,,, but wanted to check......

kwoffa
Posts: 120
Joined: Wed Nov 01, 2017 1:09 pm
CMBA Member: 1180
Location: surrey

Re: Boat Speedo

Post by kwoffa »

Hi there,
Can i trim the tube from the back of the guage,as there is a chance it maybe a tad long...at present it is not an open ended tube but has small slot and a hole...would i be changing the calibration by cutting shorter ?

Woodwych
Posts: 177
Joined: Tue Apr 17, 2012 6:05 pm
CMBA Member: 0

Re: Boat Speedo

Post by Woodwych »

The length of the tubing from the pickup to the speedo doesn't matter- so trim away.

kwoffa
Posts: 120
Joined: Wed Nov 01, 2017 1:09 pm
CMBA Member: 1180
Location: surrey

Re: Boat Speedo

Post by kwoffa »

Ah right,so i have a copper tube coming out from the guage,,,,thats what i am concerned about?....not the tubing from the pick up.

User avatar
Alacrity
Site Admin
Posts: 2193
Joined: Thu Feb 05, 2009 2:07 pm
CMBA Member: 641
Location: Eastbourne, South East England
Contact:

Re: Boat Speedo

Post by Alacrity »

I think there is some confusion here. I believe he has an different style speedo head which is NOT the style we are used to. I have one myself & have no idea what should be connected to it.

Please post a picture of what you have but DON'T cut the tube off until we know what you have. I don't think you should be cutting anything.
Mercs are like women, no 2 are exactly alike. That's what testing is about. In general it is safer to test motors and props than women!

kwoffa
Posts: 120
Joined: Wed Nov 01, 2017 1:09 pm
CMBA Member: 1180
Location: surrey

Re: Boat Speedo

Post by kwoffa »

Thanks for the input chaps,i will take some pics tomorrow.

Post Reply