Good pitch to start with on motor/hull combo?

[sutor623]

Hey guys,

I have a 1988 19' sea nymph center console. It has deep gunnels and a smaller splashwell (20"). I gutted the boat and got all the foam out and doing some rivet repair.

Anyways, the boat is 1000lbs. dry weight with a 7'5" beam. The boat had an evinrude crossflow v4 90hp motor on it. Guy said it did 30mph with 3 on board (and all the soaked foam!!) It is rated for a 140hp, so guess what I did? I bought a sweeeeettttt 1987 Johnson GT150. I absolutely LOBE those old V6's.

I have three SS props for the motor. Two are 3 blade, one is 4 blade. All three props are 24p. Dangit!! Obviously I will make a run with them and see where I'm spinning at, but I was wondering what you guys thought a good starting point is. These motors/props were well suited for bass boats which are heavier but sleeker. I think this boat is gonna scream like a banshee!!!

 

[Sea Rider]

It doesn't matter how loud will engine scream as long it doesn't over rev its max wot rpm range as usually loaded. Need to know the min-max wot rpm range for that engine factory stated to play safely with props.

Test any of both 3 blade props a a starter if being 100% exact same. If from different prop manufacturesrs could dial more or less wot rpm, only checkable on 2 different wot run test on flat water cond. Report your findings.

Happy Boating

 

[jimmbo]

WOT Rpm range is 4500 - 5500, the 24s are way too much prop for that combo.I would guess about a 19 AL would be a good starting point.
You can experiment with engine height and higher performance props, and might squeeze 2 or 3 more mph out of it.

 

[b.gagnon]

My guess would be a 21p...
I had the 17' version of that boat with a 90hp Merc. I had a 19p stainless turning 5100-5300 RPM...A 150 will make that boat very unstable at high speed! Trim tabs will be a must!

 

[jimmbo]

A 90 Merc has a different gear ratio, displacement, and prop diameters. Apples to Oranges comparison, An 19 ft boat with a 150, properly trimmed, and loaded will not get unstable and chinewalk until about 60mph. Not going to happen with a 150
Depending on load, a 17" might be a better starting point for a prop

 

[ahicks]

17 or 19 would be my first guess as well.

 

[WesNewell]

From what I found, the GT150 has a 1.86 GR. Since you already have 3 24p props, try them. Check wot rpm and go from there.

 

[sutor623]

Cool thanks guys. I will try and get a 19 off a bud and see how she does. And Jimmbo Im with you, the 19' vs 17' is a big difference. Couldnt imagine a 150 on my 17' tinny!!!!!!!!

 

[sutor623]

Fellas do you guys think a 4 blade would be a good idea on a light hull like this?

 

[Faztbullet]

round or V bottom??? I say a 20-22pitch will be close

 

[WesNewell]

Something to think about.
Your setup

• Boat type: Aluminum - Console
• Usage: Top Speed/0 ft
• Engine Manufacturer:
  Johnson
• Engine Type: Outboard
• Engine Year: 2001
• Number of Engines: One
• Engine Family: V6 2-Stroke
• Engine: 150
• Drive / Gear Case: Johnson 150-250 hp 2-Stroke 1.86 Ratio

[h=3]Details[/h]

• Calculated Pitch: 23.78
• Calculated Weight with engine(s): 2,038.40 lbs
• Calculated Engine RPM: 5,250
• Calculated Boat Speed: 53.65 mph

 

[jimmbo]

Fellas do you guys think a 4 blade would be a good idea on a light hull like this?

In a word NO, the extra blade will kill your top end even more.

You say you removed a quantity of wet foam, and did some hull repair. Did you at some point check the hull with a straight edge for Hooks or Rockers? A 1000lb boat with a V6 150 should really haul backside. Even for a tin boat a 1000 lb aounds a little light for a 19 footer.

I was running a 1998/2001(originally the Engine was 1998, then had a complete powerhead upgrade in 2001) 150 FICHT. on an 18ft Glastron it was getting about 55 mph with a 20 inch RAKER, and the engine mounted with the AV plate about 3 inches above the bottom of the hull. I know that can't be truly used as an apples to apples comparison but, it was quite a bit heavier than 1000lbs.

 

[sutor623]

Something to think about.
Your setup

• Boat type: Aluminum - Console
• Usage: Top Speed/0 ft
• Engine Manufacturer:
  Johnson
• Engine Type: Outboard
• Engine Year: 2001
• Number of Engines: One
• Engine Family: V6 2-Stroke
• Engine: 150
• Drive / Gear Case: Johnson 150-250 hp 2-Stroke 1.86 Ratio

[h=3]Details[/h]

• Calculated Pitch: 23.78
• Calculated Weight with engine(s): 2,038.40 lbs
• Calculated Engine RPM: 5,250
• Calculated Boat Speed: 53.65 mph

Wow thats awesome!

 

[sutor623]

In a word NO, the extra blade will kill your top end even more.

You say you removed a quantity of wet foam, and did some hull repair. Did you at some point check the hull with a straight edge for Hooks or Rockers? A 1000lb boat with a V6 150 should really haul backside. Even for a tin boat a 1000 lb aounds a little light for a 19 footer.

I was running a 1998/2001(originally the Engine was 1998, then had a complete powerhead upgrade in 2001) 150 FICHT. on an 18ft Glastron it was getting about 55 mph with a 20 inch RAKER, and the engine mounted with the AV plate about 3 inches above the bottom of the hull. I know that can't be truly used as an apples to apples comparison but, it was quite a bit heavier than 1000lbs.

Hey Jimmbo,

I actually did check the bottom for hooks. Luckily she looks good to go.

The weight of the hull dry on NADA says 1000, but we all know how NADA is on the older hulls. I put 3/4" floors in it and have a 200lb console. That and add 25 gallons of fuel, a 380lb motor a battery and a 25 gallon livewell and thats 1000lbs right there.

The boat called for anywhere for a max capacity of 120hp to a 140hp in its years of production. Most that I have seen have a 90hp-115hp X-flow. I have seen a couple with 120-140hp loopers. The 90-115 is around 315lbs, the 120-140 looper is 370 and the v6 X-flow comes in at 380lbs, so I figured it was worth it to size up to the v6. Anxious to see how she is gonna do!!!

 

[wahlejim]

Not to be a downer here, but have you considered that overpowering the boat beyond the Coast Guard limit is not the best thing to do? It is a limit, not a recommendation. A couple of consequences you face:

-Heavy fines if stopped
- Loss of registration/Title restriction
- No insurance company would cover any claim related to the boat (heaven forbid you are in an accident that injures or kills someone)

There was an instance near me where a guy overpowered his boat and got in an accident and there was a fatality. Insurance company investigated and denied the claim because the boat was overpowered. In addition to the guilt that he now lives with, he lost a huge civil lawsuit with punitive damages because he knew he overpowered the boat. He spent some time in jail for criminal negligence and almost got hit with manslaughter charges. He has since lost every asset he owned (cars, home, etc.) because of the lawsuit.

10 extra HP may seem like a great idea, but I would encourage you to stop and think about the consequences.

 

[sutor623]

Dude I don't think you have done your homework. There is a 10% gray area for the hp limit on boats.

Other than that my insurance company doesn't care and there are no laws in VA that dictate hp ratings.

 

[jimmbo]

I never worried about overpowering a boat, My first was a 15 ft rated for 90hp, Dealer very happily rigged it with a 140hp. I told the underwriter about the overpowering, they made a note of it on the policy and adjusted the premium and happily took the payment.
I broke no Canadian Laws. I couldn't care less what the Laws are in the US as I don't boat there.

 

[sutor623]

I hear ya Jimmbo. I think there's a lot of hearsay on the matter. I got 140 stamped on my console so I'm not blinking an eye at the 150. Honestly I will probably only open her up just to get my prop pitch right. Other than that I doubt I'll ever take her over 4000 rpms. I just like the extra torque and I found a nice 150 for under a grand and had a parts 150 of the same year just laying around. Buddy needed the 90 that was on it so he has that now.

 

[sutor623]

Ok fellas, I figured Id chime back in here and give yall an idea of what I came up with.

I have gotten the motor up to snuff and she is running great.

I had suggestions from 18 pitch to 22 pitch prop to get me where I needed to be. I actually traded the 24-25 pitch props that I had for an 18 and a 22 pitch, both rakers. I put the 22" prop on because I felt it would be closer to where I wanted to be. I had the boat set up with an average weight, me and one other, some gear and a full tank of gas(24 gallons). The boat HAULS! At open throttle, trimmed out where I want to be, the boat was moving at 54 MPH and turning 5000 rpms. Smack in the middle of the WOT range of 4500-5500.

Now, we fish tourneys in the boat also. Fully loaded and adding the weight of a bait tank, and two catfish livewells, the boat was still topping out at 50 MPH and 4800 rpms. And we will RARELY run the boat at WOT with full livewells. We also would only be running that much weight IF we catch two monster cats, and on the way back to the weigh-in.

What do you guys think, should I step down in prop pitch and try it out? I feel like I am right in swinging range here. The other prop that I have, the 18 will likely bring her up to 5800 at a light load and lose 2-3 mph. (I forgot my prop wrench at home so I didnt try the 18p)

I am thinking a 20p would be the perfect prop at this point, but I may be just splitting hairs now.........

 

[WesNewell]

I would stick with the 22p. Don't see a point in going lower pitch. If your numbers are right you're running 4% slip with it, which is pretty darn good.