Prop hub assembly or 15 spline?

[hd1shrk]

I know everyone probably is tired of prop questions. But, I am trying to understand the different types before I buy a much needed prop.

I have 1983 17' Mark Twain with the 140 and I believe an Alpha 1 outdrive. Currently there is a 14" 19p aluminum prop on it. Yes the prop is slightly eaten up in a few spots. WOT according to the gauges is about 35mph at 3500 rpm. That seems a bit slow. It does come out of the hole fairly quickly with just me and me and my kids, 290 lbs total. Before I adjusted the timing and changed the fuel filter it was difficult to get out of the hole with about 620lbs. of people and gear. That isn't normal load.

Now I have seen several different types of props out there. Ones with removable hubs, and ones that say 15 spline. Can anyone shed some light on this? Can I use either, or do I need a certain one? 21 or a 23 pitch prop? Should I do a fuel system analysis to check for proper amount of fuel? Would a chewed up prop cause cavitation and keep it from getting up to speed?

Thanks

 

[hd1shrk]

Re: Prop hub assembly or 15 spline?

Ok, I seem to have put this in the wrong place. After doing some more research, could my tach be wrong? 3500 rpm at 30-35 mph? or both be wrong? Will hook up a tach and see what happens.

 

[nitrosteve]

Re: Prop hub assembly or 15 spline?

Ok, I seem to have put this in the wrong place. After doing some more research, could my tach be wrong? 3500 rpm at 30-35 mph? or both be wrong? Will hook up a tach and see what happens.

Well I have a very similar boat as yours 1986 Mark Twain MTB 175 w/140 merc I/O same prop you have. Mine runs 36 mph at 4400 rpm. I think your tach is suspect. i just changed props tonight to a 13 3/4 x 21p SS I will let you know if its better or worse. Post up some pics of your twain...

 

[hwsiii]

Re: Prop hub assembly or 15 spline?

Hd1, if your outdrive has a 1.98:1 gear ratio you are probably turning closer to 4,300 RPM. Your tach is wrong if I have your gear ratio right. Try looking on the back of it and turning the swith bak and forth to clean the contacts and it might work right. Just be sure it is set to the same position it was before. After you get the tah working if you will get me a WOT RPM and speed we an see if you have the right prop, the one you are running is real close though. Yes a chewed up prop can ause all kinds of extraneous problems


H

 

[hwsiii]

Re: Prop hub assembly or 15 spline?

Hd1, if your outdrive has a 1.98:1 gear ratio you are probably turning real close to 4,300 RPM. Your tach is wrong if I have your gear ratio right. Try looking on the back of it and turning the swith bak and forth to clean the contacts and it might work right. Just be sure it is set to the same position it was before. After you get the tah working if you will get me a WOT RPM and speed we an see if you have the right prop, the one you are running is real close though. Yes a chewed up prop can ause all kinds of extraneous problems


H