What to do about a speedometer

jgcranch

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Just back from a nice cruise on the ottawa river - found these #s on the prop - 13x31 / 2.38 8:1 it has 4 propellers -Could anyone explain what if anything these #s mean? Also had these results - at 3500 rpm 14.7 mph - WOT 5200 rpm 27.3 mph with my wife and Dog with me / 1/2 tank gas and no wind -as a new member will post few pictures of boat as soon as I figure out how to do it
Hi Allen I believe the first number is the diameter and the 2nd is the pitch. I think the 2.388:1 is the gear ratio for the command thrust lower unit. We were out yesterday also and rechecked my speeds. I had 13.8 mph at 3300 rpms and 21 mph at 5200 rpm which was wot. I thought that the rpm and speed were both higher in the past. The trim did not seem to affect performance much.
 

Allan56

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Hi Allen I believe the first number is the diameter and the 2nd is the pitch. I think the 2.388:1 is the gear ratio for the command thrust lower unit. We were out yesterday also and rechecked my speeds. I had 13.8 mph at 3300 rpms and 21 mph at 5200 rpm which was wot. I thought that the rpm and speed were both higher in the past. The trim did not seem to affect performance much.
Hi jg - thanks sounds right -as you say our speed difference is probably due to my lifting strakes - also have 25” toons - if you have 23” - that might affect speed I don’t know for sure though
 

jgcranch

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Hi jg - thanks sounds right -as you say our speed difference is probably due to my lifting strakes - also have 25” toons - if you have 23” - that might affect speed I don’t know for sure though
ma


I do have the 25 in pontoons so the prop and the strakes are making a significant difference in the speed. The dealer said it should go 24-25, and strakes would add a 1 -2 mph difference with the 90 hp when I was looking at purchasing a new one but then I found the one I have , a 2017 with only 40 hrs on it and a savings of $6500 from a 2018 so I figured it was a good deal. I cann't add the strakes now but I am going to research the prop since i am going to purchase one anyway.
 

ImTinkerbella

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Hi Allen I believe the first number is the diameter and the 2nd is the pitch. I think the 2.388:1 is the gear ratio for the command thrust lower unit. We were out yesterday also and rechecked my speeds. I had 13.8 mph at 3300 rpms and 21 mph at 5200 rpm which was wot. I thought that the rpm and speed were both higher in the past. The trim did not seem to affect performance much.
Just wanted to throw my hat into the ring here, J and G...

Yesterday was our first day back out on the water since I returned from my trip, (and my husband returned from his various business trips).

We have the same engine as you, as well as the same prop. (Which I received a quick education on and have the part number memorized now as we trashed our original one on a wing dam day two of taking new ownership last year. Black Max 48-78114A45 16 x 13. I put them on price alert through Amazon, and when the price drops to my desired level, I buy as there are underwater "landmines" sitting in wait to destroy props around here. Insert **eye roll**)

Anyway, I digress... Yesterday morning -- before the winds kicked up -- at WOT we topped out at 22mph.

I know you live in the same area as we do, so I suspect with all of the "biological growth" which dominates during the summer (and sticks to the toons, gets caught in the prop, et al), that is likely the top speed one can expect out on the main channel.
 

jgcranch

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Hi thanks for your input and glad to hear from you. We are going to Crater today (hopefully there will be room) and I am going to try out a new prop. I will post the results.
 

ImTinkerbella

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Hi thanks for your input and glad to hear from you. We are going to Crater today (hopefully there will be room) and I am going to try out a new prop. I will post the results.
Have fun!

It was nearly empty when we went past there yesterday morning, but literally jam packed (largely with houseboats) when we returned. Glad we elected to head out to a very small sandbar in a wildlife preserve area, as there is realistically only room for one other boat there.
 

jgcranch

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The new prop gave a speed of 24.3 mph (gps) at WOT of 5900 rpms it is a four blade 14 X 12. It also gave a quicker acceleration
 
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