Get me in the ballpark

[dcain1979]

I am running a 1986 Laser with a 1989 mariner magII moror. The hull is the tunnel hull type. It has a 6 inch jackplate. I am running a 26p laser II prop.

The prop has a decent hole shot, but blows out slightly when the bow starts to fall. I am turning 5100 rpm at wot at 52 mph. I have moved the jackplate up and down but have had little to no results. It throws a 10 ft rooster tail everywhere I have set it so far. I have no Idea where to start with the prop selection since it is a tunnel hull boat. What are some reccomendations on where to start would be.

Thanks.
Daniel

[David]

52 doesn't seem fast enough, but 5200 rpm is close to peak power for that engine. My old Virage modified tunnel ran around 70 with an XR4, the Merc equivalent of your Mag II.

1. is the boat core wet?
2. does it have a hook?
3. how high is your rooster tail?

I needed a lot of setback and a prop with more bowlift than a Laser to make my Virage fly.

Try a 26 big ear Chopper or a Hoss Hyperdrive or something with a lot of bow lift.

[150aintenuff]

try a 26 trophy + or 26 Chopper laser 2 is not a good surfacing prop, good for slower hulls with engines buried tho.. I just sold a TR04 that would have worked VERY well in your aplication.. pushed a sleek craft SST 76 with a yamaha 200.. LOTS of Lift EVERYWHERE.. something similar to that would be my pick... also set your engine so it is 2.5" low in relation to the pad.. jack up from there.. you ALSO may be over trinmming it a touch.. cause your prop is free loading the engine and as a result you have about 35% slip.. i get 48-52 mph out of a 2.0:1 ratio equiped 150 running a 21P prop... you have more shaft speed pulling a bigger prop at the same speed.... not good........

10' rooster is WAY to tall... cowling high is general rule.... length is a big variable however..

[dcain1979]

As far as I know the core is not wet and does not have a hook in it. I did not take the boat out for a test ride, since it was 500 miles from me. My dad did take it out though and said the gps speed was 71 mph, with a prop that did not go with the boat. The prop that I got with the boat was the laser II.




ok, I was talking to the gentelman at the local prop shop. He gave me a 25 tempest to try, I tried it out and it was definatley better but not exactly what I was looking for. I was turning 5700 rpm at 58.7 mph. The prop had good holeshot and decent lift. I am not exactly for sure what the redline is on the engine but I am thinking that 5700 is pushing the envelope. But when a 170 passenger was put into the boat it killed it. The boat still had a good holeshot, but it seemed to have lost the lift and was back down to 5200 rmp and 52 mph.

Is it safe to assume that I am basically wasting my time trying to get the tempest to work correctly on my boat?

[David]

A second passenger kills speed? Well, that's my experience with an underpowered tunnel, which is what you have. But you should be able to make it fly pretty good solo.

I don't know much about the Tempest. People use them on bass boats, but probably not at the engine height you are trying.

My XR4 (same motor) bogs off idle with a Trophy, even with the vents removed. Is your engine the small hub? The big hub engines work well with the small hub Trophys.

But you should be able to find a big ear Chopper relatively cheaply. If you have the small hub you will need to remove the weed cutters.

[dcain1979]

I'm sorry i did not specify, this is a fishing boat. Anyway, the engine is a big hub engine.

What is the difference between a big ear chopper and just a regular chopper?

[150aintenuff]

Mod VP tunnel is a mod VP tunnel doesnt matter what you are using it for... a big ear chopper was for a V6 4.75" gearcase, a small ear chopper was for the XR4/Inline 4.25" gearcase.. what pitch was the Laser2... even # pitch are small hub or 4.25" you should see a small gap between the outer edge of the barrel and the iner edge of the gearcase. LAser 2's shouldnt be ran much more than 3" below the pad.. Tempests dont like that much height either... trophy or Chopper IMO..

where are you located.. I have a 24" bigear chopper forsale, if ya can try one and find out will make a deal on it..

[dcain1979]

The laser II is a 26 pitch. There was a gap between the prop and the gearcase. I am gonna see if I cant get my hands on a chopper and try one out. The trophy props that you are also reccomending are they a 4 blade prop?

I am located in North Carolina on lake norman.

Have you guys ever heard of a big ear tempest prop? The previous owner says that is what was on the boat when he and my dad carried it out. I have never heard of one though.

Does anyone know what the redline on this engine is. 1989 mariner magII. I am getting a couple of different things from people

Thanks for all the help that you guy are doing.

[150aintenuff]

no rev limit.. powerband seems to fall off at around 5700-6000 though.. you do have the big gearcase.... must have been ordered without the 1.78 or changed over at the dealer.. SO Trophy is a 4 blade... there are 2 trophies.. is NLA and it is a big hub the second is a trophy + and its a small hub both are excelent props.. a Tempest is a 145/8inch 3 blade..

trophy in 24 or 25 p would be my recomendation If you wanted I would LOAN you a 24 Chopper if you wanted and were willing to pay shipping both ways.... runs about 20 bucks or there abouts.. its not exactlly perfect but would give ya an idea how a chopper would run on it.... then you could get a better one if you so desired..

[pyro]

I think the 89 magII has 1.87, I thought it was just the 2.0 liters that had the 2:1, such as the '86 & '87 XR2. I calculate 25% slip with 1.87 and 18% slip with 2:1. Either way, it's too much. The Laser II sucks, not designed for jackplates and surfacing, it just slips like hell. I'm surprised you're not getting more RPM and top end than that, even with a sh**ty prop. I would expect more like 65+ with that setup.

[150aintenuff]

your right.. i was thinking XR2.. my bad.....

[David]

The Mag II came came out in 88, and was pretty much the same for 89. The Mag II was the 2.4L with the 1.78 gearbox. So his gearbox has been changed.

Big hub motor, small hub Laser, that explains the ventilation coming onto a plane. My Laser didn't work well at high engine heights on my Virage. It isn't any better at high heights on my Allison.

Big hub motor, small hub Trophy, that should work. The Trophy can be run high and has good bow lift.

I'd still try a Chopper for top speed. Most are big ear, which will fit the big gearbox with or without weedcutters.

Maybe try a whale tail of some form so the boat will plane without ventilating too much with the chopper.

[dcain1979]

First off, thank you all for the information that you guys have been giving me, you have been a huge help so far.

I am going to go on a search tomorrow at some of the local prop shops and see if I cant get my hands on a chopper or a trophy and give them a try.

npartin, thanks for the offer, if I cannot find one locally I might take you up on the offer. I am going to try and find on locally tommorow.

Is this changing to the larger gear case a routine thing to? Is it supposed to be a stronger gear case?

So throw the redline out the window, what should this motor be capable of turning before parts start flying out of the cowling?

[pyro]

6500 should be safe, prop it to turn 6300 and you should have a good balance of acceleration, top end, and motor longevity.

[150aintenuff]

1st make sure its firing on all 6.. I have had a plug wire come off and it sounded fine just wouldnt pull more than 4400 with my setup.. (5300 max RPM) prop it to 6500 MAX unless you want to remove the oil injection, Mix your own fuel at 32:1 and be ready to replace bearing and ringe every couple hundred hours... the gearcase was changed for whatever reason( may be it broke) maybe it was ordered with the big case.. who knows.. it was a common change though there is LOTS of 1988-1990 XR4 motors here that have the 1.87 swaped on to them because they were used on heavier boats that the 1.78 ratio couldnt get a prop to work on.. so if it was on a heavier boat that would explain the swap over to the big case..

[David]

I would prop it for 6000-6200. My XR4 has never turned more than that with any prop. It just runs out of power. Then you can keep the oil injection and run regular fuel. Hassle free.

There is an spark timing retard box on your motor. You won't see 6500 rpm unless you are way under propped.

[150aintenuff]

the spark retard is fixable... if it remains prop for 5700-6k.. otherwise 6500 is where I would set it at...

[dcain1979]

Thanks, again for all the replies. Unfortunatley this crazy weather had my sinuses all messed up this weekend and i barely left the house. I am going to try and find a chopper to try in the morning before work.

The previous owner pulled off the oil injection so I already mix it.

[dlivewyer]

Here is a reference chart that has the xr4 on it as well as others.

RPM chart (http://www.kencook.net/Gears.html)

I have an '89 xr4 that turns 5600-5700 with a 24 trophy plus.

I don't know if it would turn 6000-6500. :eek:

How much does the boat weigh?

[dlivewyer]

otherwise 6500 is where I would set it at...

How would set it at that? :confused:

[T-REX]

Soundz like ya bote iz waterlogged!!!....That iz very typical fer a Laser LTV....It will not run full ov water!!

[stokernick]

hey,Rex,thanks for the speedie response!!!!!!!!

[T-REX]

Betta late than neva......or so they say!!!:D :D

[stokernick]

I thought it was better never late!