WOT Turbo 2+2 4 Blade

[va1968sh]

For the past 21 years I have ran turbo props and if possible, I need someone's expertise regarding a Turbo 13.75 x 22, 2+2, OT, 4 blade prop. Back in April, 1987, I purchased a 1987 Ebbtide Dyna-trak 180 STE, Johnson 150GT, 18 ft boat. The boat was equipped with a Turbo 14.25 x 24 and was very fast; 5400-5600 RPM?s and somewhere in the upper 50?s, close to 60 MPH; the speed was showing 65MPH but that's not accurate.

The power band was mid to upper range and I decided to go with the 4 blade 2+2, referenced above, in 1989. The hole-shot is great and it is fast till about 4500 and then the RPM max out at 4800-to maybe 5000 on a good day. Normally I fish alone and run about 10-12 gallons of gas. The boat runs great till the rpm?s I referenced and that?s it! I have raised the engine to the top hole???..it was one hole lower back in 87-89. Than may have helped a hundred or so RPM?s but not much. The water pressure is about 18 PSI by my gauge. I do not run a jack or set back plate.

For my question, let?s assume the motor running ok, which it has always, 120+ compression, never has done anything but run perfect, tachometer is accurate. Back in 1987, the RPM range recommended was 4500-5500, but I have noted on several boating forums discussion about WOT being 5600-5800 because of fuel. They advise running in the RPM range I run is bad because of today?s fuel. I think dropping the pitch may not be the answer? I have thought about a jack plate or set back plate; maybe you know of a set-up for the old Dyna-Trak 180 STE's?

I think for my application the 2+2, 4 blade is the correct prop but the WOT RPM?s concern me. Maybe you have some recommendations? for many years I have never ran the RPM's I expected based on the 24 3 blade Turbo it had back in 1987. This boat has always been garaged and babied for over 20 years. Maybe I have unrealistic expectations?? You ask why now am I concerned???????I?m getting back into bass fishing and have a almost new, 21 year old boat.

Regards,
Sid Helms

 

[va1968sh]

Re: WOT Turbo 2+2 4 Blade

Sorry for all the information. I think the issue is the mounted height of the 150GT. When I ran 3 blade, 14.25 x 24 prop, it was mounted in the 3rd hole of 4 possible mounting positions. Now it is mounted up in the 4th hole.

The boat has what I will call an off-set in the bottom rear of the hull. If you follow the the bottom of the hull from the front, about 2 feet or so from the transom, there is an off-set up of about 4 to 6 inches, about 2 feet wide to transom. this is in direct line with the engine lower unit and prop. The cavitation plate, with the engine in the top hole, is about an inch below the bottom edge of the transom\off-set. The off-set is higher than the bottom of the boat, up from the water surface.

So the current 4 blade is running higher, one hole up, than the former 3 blade that ran so good on top-end. Since the 4 blade is a 13.75, maybe I should have went down a hole instead of up??? With the "hull off-set" at the transom, I am not sure where the cavitation plate sould be? I read about starting 1 inch up fron the bottom of the transom. For my hull, could it be 1 inch up in the off-set? With the engine in the top hole, it is slightly below the edge of the transom, in the off-set. Is what I call an "off-set", a pad or ride pad?

Thanks for any help.

Sid Helms

 

[va1968sh]

Pictures of transom & motor

Pictures of transom & motor

Here are pictures of the lower transom area and motor. The 3 blade Turbo was 1 hole lower and was fast. Motor trim is lowered all the way.

I had to down-size the pictures. If you are interested, I can email you the larger files.

Can anyone help??

 

[va1968sh]

Re: WOT Turbo 2+2 4 Blade

I have lowered the motor one hole, like it was with the "fast" 3 blade Turbo. I think the prop was too high and it was not lifting the boat as it should.

I will test it tomorrow. Also, I am considering a CMC jack plate. The transom shows no problems but I am considering reinforcing the engine mounting area with a 3/8 to 1/2 inch aluminum plate.

Any thought to this entire post is welcome.

Thanks

 

[codertimt]

Re: WOT Turbo 2+2 4 Blade

It seems like you have all the basics down, so I'm not sure I will be able to really help much...but I'll go ahead and offer some comments based on setup research I've done in the past.

First off, why are you stuck on the 4 blade? It seems like it was setup pretty good for top end with the original prop when you got the boat "back in the day". Unless the holeshot was unbearably slow with that other prop, it seems a similar replacement might be the ticket...

Now here's a rundown of my assessment of you're current setup. Experts, feel free to jump in and correct anything incorrect...

1. 4 blade props generally will cause a drop in rpm. Even with a drop in pitch you're seeing a massive drop in rpm, so it seems like your boat/motor combo don't like this prop...but perhaps it's still a setup issue...
2. When running a 4 or 5 blade for speed type applications, generally you want to run it as near the surface as you can...I think the idea is the extra blades gets more bit, so can run nearer the surface without ventilation. So raising the motor was correct in this regard...
3. However, raising the motor too much can affect how much the bow is raised from trim. So it's true that lowering it might get the bow up more, but with the prop deeper what it actually does for rpms is up in the air...so your experiment is about the only thing you can do.
4. With a boat that has a pad, I've read the starting point in height is the cavitation plate 3 inches above the bottom of the boat.

Anyway, as I stated in the list, it seems to me that your boat and this particular 4 blade don't get along well. But I should probably reserve judgment on that until you get a test run in with the motor in it's original location. Maybe the bow and rpms will come up for you nicely.

Overall, it seems like you have everything under control. I'm sure someone with more experience with this application will come along, but until then, keep experimenting and keep us up to date...

 

[steelespike]

Re: WOT Turbo 2+2 4 Blade

I know nothing about the technology of your props.But the first thing they say about a 4 blade is it will lower your max rpm.It would seem to me if you don't have any ventilation problems your not too high.Usually a 4 blade is all about low end performance.Antivent plate height is not set at a hard demension you simply raise the motor to a point just before venting becomes a problem.
I would guess the 4 blade may not have as much lift at higher rpms.

 

[va1968sh]

Re: WOT Turbo 2+2 4 Blade

Thanks so much; it has a great hole shot and goes like a bullet till 4700 RPM's and that's it. I will admit the 3 blade was fast but all top end and it was a wild ride. The 4 blade does what I want but I think the RPM's are off about 300-400.

And the biggie........steering torque but I solved that with Hyd. Sea Star steering. To be truthful, I wish I could find the 14.25 x 24 I had in 87.

I'll let you know what happens and thanks