Prop Advice Please

[Turkey]

I have a 17" glass bass boat with a Mercury 150 XR4 on the back of it and I need some prop advice on what prop I need to get. I'm seriously over reving the motor turnning 7000-7300 rpm WOT running 60-65mph. I understand this is bad..I unfortunatly don't know the diameter or pitch of the current prop as it came the boat. All I can say for sure is it is Stainless and Ballistic is either the model or manufacturer.

I don't really need another stainless, aluminum actually might work better because I fish a lot of stumpy lakes. But I have no clue what kind of prop to look for, 3 blades or 4 and what pitch? I don't have a lot of money right now but I plan on using the boat a lot this season and need to address this asap.

Also are refurbished props any good? I may end up going that way or possibly trading my stainless for an aluminum to lower the price some, is this a good idea if I can get the prop refurbisher to do it?

This is my first boat and don't know a lot about them in general so any help/advice would be greatly appreciated.

 

[Ron G]

Re: Prop Advice Please

i would stick with stainless you need something around a 24 or 25 would guess,im amussming this is a bass boat.

 

[Turkey]

Re: Prop Advice Please

Yes it is a bass boat, glass hull, v bottom 17' more or less. I've been out asking questions and all that has done is create more questions. I pulled the prop today and took it up to my fav prop shop and they measured it for me and it turns out it is a 21p. not sure of the diameter though.

The guy at the prop shop ((McGills Prop and Welding in Lewisville, Texas) not sure if naming names is allowed, I appoligise in advance if it isn't) was nice enough to spend a lot of time with me answering questions, but he only knew so much so I need you people some more.

New questions...

The prop guy thought that the tach may be reading false, that that xr4 would have eaten itself by now if the tach was correct, is that a possibility? The motor sounds like it was wrapped pretty tight at WOT so it is a serious concern, but shouldn't it have hit a rev limiter?

The service guy where I would take it is booked for a month solid and the only guy he has that works on motors as old as mine is only part time, he said he normally won't touch them that old. He did tell me he thought that it is possible for a tach to be wrong but said it is possible that it is wrapping up that tight but can't say. (perfect repair shop answer)

It would cost more to have the tach checked/replaced than I can get an aluminum prop or refurbished SS prop for. I'm leaning on going that way, just slap a new prop on there and watch the speed and rpms looking for an increase in one and a drop in the other, is this the correct assumption if the tach is showing the true rpm reading?

Depending on the answers I get for these two I'll know what questions I have later. I'm not sure what to do at this point...I want to make the cheapest right decision, as the funds are rather limited right now.

I do a lot of stumps and don't have a keyed prop, it is splined and I am paranoid about breaking the output shaft on the LU. I know this is probably the least of my worries but it is still valid. If the tach is accurate I would need at least a 27p to cover the extra rpm figuring 400rpm per pro size increase. I'm so confused, this is a great motor runs great runs really strong and runs all day long...starts easy hot or cold. I don't want to ruin it.

Thanks again for the help!!

 

[Ron G]

Re: Prop Advice Please

1st of all it should'nt cost that much to verfiy a tac.!!!and that needs to be fixed before anything else that and the water preassure gauge is the most important things.and yes it is quite possible to wind a 150 merc up to 7000.

 

[kenmyfam]

Re: Prop Advice Please

Verify the tach. Job #1

 

[Turkey]

Re: Prop Advice Please

Any recomendations on getting that tach verified? I mean I am pretty sure it is accurate or at least close. I mean this motor keeps pulling to wot, and wants more, but if you adjust trim it screams...but a few degrees on trim and it just wants to pull harder and go faster...If it was on wheels, I would say that the motor has a lot more to give, and wants to give it. I don't think it is an inaccurate tach...

I bought the boat used. It is old but under the cowl looks bran new, stock paint and wiring. I can spin the prop in a hole shot if I'm not careful, so I'm thinking I have a jewel or a cubix...all I know is the guy I talk to that has driven it says it needs a 4 bladed prop with a 25 pitch minimum. I need to verify that with others that have had this motor in great shape.

This thing is really nice in how it runs and allways pulls...it runs that 7k plus rpm and seems like it wants more...anyone in DFW that wants to run it let me know.

If you think you can help I'll meet you at any lake within 50-100 miles of the DFW area.

 

[NathanY]

Re: Prop Advice Please

My tach was bad on a brand new boat, took it back to cabelas and they fixed it. If you are anywhere near DFW, take it to North Texas Marine on 820 in Saginaw, and ask for OPTI, he is the best Merc mechanic in TX.

 

[Dhadley]

Re: Prop Advice Please

What's the diameter of the prop you have? It's a 3 blade, right?

 

[Ron G]

Re: Prop Advice Please

By the way what kind of hull you got??Brand name?

 

[Turkey]

Re: Prop Advice Please

I believe the dia of the prop is 13 3/4 but might be a 14 1/4, would need to verify, it is a 21p 3 bladed ballistic, and all the ballistic props I have seen listed for this motor are 13 3/4. It does have the smaller of the 2LU's on it. The hull is a Pleasure Craft 168 '89-'90 year, it is a bassboat with a v-hull. I'm thinking about jumping to a 25p prop and switching to 4 blades rather than three. I'm not certain this is the best idea but going on the assumption that the pitch will drop the engine 200-400 per size, that is the best one to try first. I really can't to replace it more than 1 time unless I wait longer and I have kept it out of the water far to long allready.

I would appreciate your opinion on that plan of action, there is more discussion on it from the engine side of things in the merc/mariner topic.

Can't say it enough, thanks for all the help. Just messing with this prop is teaching me a lot about outboards...I come in here to check for updates and spend time reading all the trouble threads...lots a great people in here with a lot of knowledge.

 

[Dhadley]

Re: Prop Advice Please

If you have the small gearcase you'll have a 2:1 gear ratio. Where are you located?

 

[Turkey]

Re: Prop Advice Please

I've been told that the ratio is 1.78:1 (small) and 1.84:1 (large) (if I remember correctly) on this motor. I'm in Texas north of Dallas.

 

[Ron G]

Re: Prop Advice Please

Carry it to any shop and varify the tac just to make sure.then i bet Dale and i are thinking on the same lines.im not familiar with your hull does it have a pad on it?are youinto going fast or water sports?sounds like a strong motor does it have a lowwater pick-up on the lower unit?

 

[Dhadley]

Re: Prop Advice Please

A 1.78:1 on a 2.4 Merc? That's odd, but whatever it is, it is.

7000 rpm at 60 mph with a 21 on a 1.78 = about 24% slip.
With a 1.84 = about 22%.
With a 2.00 = about 15%.

Count the propshaft turns and let's verify what ratio it is.