Speed question

[Northfl]

For all you other m/a owners out there. I have a 99 ma18 with a ox66 150 on it. The prop is a 14.25x19 rapture 3 blade. With a full tank of fuel and by myself turning 5300 rpm wot i am getting 40mph according to the gps. Trimmed out and jackplate up about 2.5”  does this seem slower than should be or about average. Questioning because i was think about maybe getting a new prop if this one isnt the right one. 

Thanks

 

[Nag Juice]

Get a 14.5x21 three blade. You will see better numbers. I think a OFX3-19 would be ok too

[Northfl]

Nags will that maintain a comperable hole shot or maybe a better one??

[whichwaysup]

I was getting 53/54 on my 18MA, same engine.  Not sure of prop size though!

[Northfl]

Before i bought the boat i went and ran it with the previous owner. With almost an empty tank we did hit 53 by gps with the two of us in it. But again the fuel was almost empty. Since then i havent been able to hit anywhere near that speed with a full tank or almost full tank by myself. Both of us are around 200 pounds and i figure 40 gals of fuel no more than 350, less another 200 lb person that adds 150 extra or less. Would that 150+/- make that much of a difference?? Maybe i am doing something different than he did  motor down lower? Maybe it gets squirrely if i come up anymore   Maybe i should just be ok with 40ish mph.  i dunno , and i am ok with 40 but if i can get that without turning the rpms even better i suppose

 

[Nag Juice]

1 hour ago, Northfl said:

Nags will that maintain a comperable hole shot or maybe a better one??

The better hole shot was the smaller diameter. The OFX was a pig for my F150. 

[Moderator]

Did the seller take off the speed prop and put on a spare ?  It sounds like a different prop:  53 mph and now 40..

Try a different 19 pitch 3 blade..  The Yamaha Pro series was a fast wheel.. Maybe you can find someone to loan you one up there..

M-1

[hurricane]

I have an 03 18 MA, with 150 vmax carb'd motor, no jackplate. I run a Powertech OFS319, run 5500 at 53mph. Good holeshot and cruise 3500ish at about 30-32 mph.

[triplec]

I am not prop expert but sounds like you need to play around with some. Thats a strong engine on that hull and should be in the low 50's. Mine is a 96 with a heavy double rod locker cap and similar but older engine. I run a 4 blade prop though and gained hole shot and handling but lost some mph. It will still run around 50 though. It is a Power Tech PTC4R18PCL200. I would say run your set up by Marcus at Power Tech and get his thoughts.  

[Northfl]

Thanks for the input. I will ne looking into the options and post the results when i figure out what i am gfoimg to do

[Nag Juice]

 

[Drummer]

I love to check basics first.  Are your trim tabs all the way up and is your motor tilted but not cavitating?  

[cjk]

I have a 1998 18.5 with a 98 yamaha pro v 150. I get 53 to 54 mph top end light at about 5700 RPM. With a fishing load I usually get 50mph at 5400RPM. My prop is an older Turbo brand prop that a prop shop told me is 18 pitch, but reads 19 pitch with the cup in it.

When I purchased the boat back in 2011 it would only top out at 5000RPM and mid 40s. The only thing i did to it to get the above numbers was new spark plugs. I would start with new plugs and a compression check on the engine. Then I would make sure the carbs are clean. You should be getting more speed and RPMS than that.

Hope this helps.

[Northfl]

thanks for all of the replies. I will take them all into consideration and get this figured out