Did I choose the wrong prop? 20ft Bryant w/19p

[AlmostFamous]

Hi,

On Sunday I took out my new to me 1994 Bryant 20ft bowrider for a test run with my new prop and I was disappointed with the results.

-5.0Fi Volvo Penta with SX outdrive (yes, yes I know it's a Ford and they are no longer supported)

-New Solas Rubex 19p 4-blade prop. Aluminum

I felt the boat was slow to get on plane, even with WOT and trimmed all the way down.

Top speed with 3 people just less than 1/2 tank of fuel (20 gal.) I got about 36mph at almost 3,800 rpms. I didn't have her completely trimmed out, but def. within reason IMO.

The boat came with a ratty 17p Aluminum 3 blade. The manual makes no reference to what was stock.

The engine runs smoothly and starts quickly. I verified that I'm getting WOT at the throttle body, a quick blip of the throttle when running in neutral confirmed this. I will go through and replace the fuel filter, cap rotor, plugs and wires to be sure. I've also got an EEC-IV scanner on order to check for any trouble codes.

From reading what others have posted about their 20-21ft boats with similar power plants, I assumed the 19p 4 blade would be about right. Am I wrong? Should I stick with a 17p ?

 

[aerobat]

Re: Did I choose the wrong prop? 20ft Bryant w/19p

depending on the gear ratio in your drive a 17p may indeed be the right choice. assuming the engine is healthy and the boat not waterlogged your prop seems to be to big for the given boat/engine/gearratio .

 

[steelespike]

Re: Did I choose the wrong prop? 20ft Bryant w/19p

19" doesn't seem excessive its right in the middle of the list. There are 2 5.0; a 190 with a 1.66 ratio and a 215 with a 1.60.
You need to make up 800 rpm.That's about a 4" drop in pitch putting you at a 15" That does seem extreme.
I don't think a blip of the throttle can do much to tell if it opens all the way.Any motor with no load will rev easily to 6 or 7000
or more depending on your determination.Of course yours probably has a rev limiter.You need to look at the throttle plates or at least the linkage.
Check the compression,when you remove the plugs note the location and condition.
Normally a 2" drop in pitch nets about 300-400 rpm so doesn't seem the a 17" would be enough.

 

[aerobat]

Re: Did I choose the wrong prop? 20ft Bryant w/19p

lets do not forget that he has a 4blade 19p . most probably a 3blade 17 pitch fits since the gear ratio is high at your engine.


36mph speed lets me believe the throttle opens all the way , but check it .

 

[Philster]

Re: Did I choose the wrong prop? 20ft Bryant w/19p

Something still seems off. The move down to a 3B 17p doesn't seem like it's enough to make a substantial leap forward. He's off by too much.

There is still cause to investigate the engine and the hull at this point. Engine compression, health, etc and Bryants have always been cored with wood I believe, so that might be one heavy boat if she is waterlogged.

 

[aerobat]

Re: Did I choose the wrong prop? 20ft Bryant w/19p

but the difference between a 4blade 19p and a 3blade 17p will be significant , far more when both props would be three blade, further the engine, when stucked at 3800rpm , is far away from developing the rated power it would develop at 4600 which worsens the situation.

 

[zagger]

Re: Did I choose the wrong prop? 20ft Bryant w/19p

What kind of performance did you get from the 17" 3 blade prop? I would think that even with a 19" 4 blade prop the motor should be revving much higher if it would be healthy. Checking codes and compression on the engine would be first thing I would do. Also since it is a FI I would look at the injectors, fuel pump and filter. On your next outing swing by a truck scale and verify you are not carrying extra 1000lbs of water logged in the hull. Any one of these things could severely impair your performance.

 

[aerobat]

Re: Did I choose the wrong prop? 20ft Bryant w/19p

afaik the sx drive was delivered with multiple possible ratios and thats the mess. when he has a 1.6:1 the 19pitch 4b may be simply to much , the ford 5.0 is rated at just 220hp on the shaft when i,m correct.

without knowing the ratio for sure its hard to quess something, also the weight of the boat is interesting- and the danger is to start screwing around on a healthy engine and mess something up.

my experience is that when the engine sounds and feels right it is right, you can save the time in checking compression, spark advance etc.

like written a waterlogged boat or a hull with massive growth is also a classic for low performance.

when the boat came with a 17p 3b and now he installed the 19p 4b my best guess is he has not any issues with the engine but simply a high gear ratio and ordered the wrong prop for this.

cheers !

 

[AlmostFamous]

Re: Did I choose the wrong prop? 20ft Bryant w/19p

Guys thanks for the great suggestions.

I verified that I am indeed getting WOT at the throttle body last night. ie, looked down the bore and saw the throttle plate.

The code reader came last night, I performed the KOEO and KOER tests. Both tests returned a code 11, System OK.

I replaced the fuel filter/water separator last night, according to the label it was last replaced in 2009.

As for the condition of the boat, I'm the 3rd owner. The PO purchased it from a dealer in 2009. It appears to have always been stored inside and on a trailer. The hull is clean. I've learned a lot from this site about what to look for in a used boat. I don't see any indications that she's waterlogged, but i can scale it out this weekend for the heck of it.

I've never used the 17p 3 blade on the boat. The PO bent one blade badly on a rock . It does not appear fit to use in my opinion. I did find what I believe is the original prop last night. It's a 3 blade 19p aluminum.

I'm starting to think I did order the wrong prop based on what you guys are saying. What about a 4 blade 17p?

 

[aerobat]

Re: Did I choose the wrong prop? 20ft Bryant w/19p

I did find what I believe is the original prop last night. It's a 3 blade 19p aluminum.

I'm starting to think I did order the wrong prop based on what you guys are saying. What about a 4 blade 17p?

hey !

yes, i as mentioned also think so . my recommendation would be not to screw anything more on the engine since i,m pretty sure you have not an issue with this.

when you say you reach 36mph and 3800rpm with the 4b 19p i think you will end up at 38-39mph and ~4100 rpm with the 3b19p you found. when the prop looks ok just install it and report the results before bying another prop .

a 4b 17p should bring you in a similar region, maybe a little more rpm,s .

also do not forget to trim up when on glide .

cheers !

 

[Philster]

Re: Did I choose the wrong prop? 20ft Bryant w/19p

but the difference between a 4blade 19p and a 3blade 17p will be significant , far more when both props would be three blade, further the engine, when stucked at 3800rpm , is far away from developing the rated power it would develop at 4600 which worsens the situation.

Not to nitpick, but it doesn't matter if the engine makes peak power at 4600. When it makes that power, it's overcoming all associated variables at the speed at which it is attaining it. It's not as if not reaching the peak power RPM is preventing a shift point or something. Then it'd matter.

He's gonna likely fall short of 4600 by dropping pitch and blade count. What are we saying is the RPM range we need to get into?

 

[AlmostFamous]

Re: Did I choose the wrong prop? 20ft Bryant w/19p

If I recall correctly, the owners manual says 4200-4600 rpm . I'll double check when I get home tonight.

 

[aerobat]

Re: Did I choose the wrong prop? 20ft Bryant w/19p

Not to nitpick, but it doesn't matter if the engine makes peak power at 4600. When it makes that power, it's overcoming all associated variables at the speed at which it is attaining it. It's not as if not reaching the peak power RPM is preventing a shift point or something. Then it'd matter.

ahoi ! not sure if i understood your post right, but the the engine develops its 220horses not at every rpm but at 4600rpm ( due to the manufacturer) at just 3800rpm it develops less horses than 220 . the prop absorbes the power the engine puts in and develops by doing this thrust which moves the boat. the WOT rpm occours when the power absorption from the prop equals the power the engine can give at a given rpm. when the power available vs power absorbed equal occours at 3800rpm in the end effect less horses are put into the water which makes the boat go more slowly.

with other words : a too high pitched prop which absorbes more power than the engine can give to rev it to rated rpm REDUCES the boat speed, even when you are right that there is no "shifting point" at boats- and because of that we have a WOT rpm range given by the manufacturer.

a rpm range of 4200-4600 seems correct to me.

 

[Philster]

Re: Did I choose the wrong prop? 20ft Bryant w/19p

You don't even need to know the HP rating. It is irrelevant.

If an engine can spin at 3900 RPMs, the gearing dictates the prop speed.

If an engine can spin at 4600 RPMs, the gearing dictates the prop speed.

An engine can spin at a certain RPM given a certain load because of the power it makes, but getting to that magical peak HP RPM doesn't mean you are tapping into something more than the prop can deliver.

The HP at 3900 RPM allows the engine to turn the prop a given number of spins. The engine has the internal working strength/breathing to run at 4600 RPMs, but you can calculate all the speeds based on gearing (includes prop as the final gear) alone.

If the engine made 220 HP at 4600 RPMs or 600 HP at 4600, the prop and gearing are going to return the exact same speed.

 

[bnicov]

Re: Did I choose the wrong prop? 20ft Bryant w/19p

As long as you are operating in the recommended RPM range, you are fine. Now, that said, you are 4-800rpms off of the top end. Make sure the prop you are using is also the right size as well as the correct pitch. Check on turningpointpropellers.com, they have a prop recommender. Also, your tach could be off. Beg, borrow or steal a shop tach to verify that yours is accurately reading at WOT. Your local prop shop can also be an asset, you may be able to borrow a prop or two to see what works best. Good luck.

 

[AlmostFamous]

Re: Did I choose the wrong prop? 20ft Bryant w/19p

As long as you are operating in the recommended RPM range, you are fine. Now, that said, you are 4-800rpms off of the top end. Make sure the prop you are using is also the right size as well as the correct pitch. Check on turningpointpropellers.com, they have a prop recommender. Also, your tach could be off. Beg, borrow or steal a shop tach to verify that yours is accurately reading at WOT. Your local prop shop can also be an asset, you may be able to borrow a prop or two to see what works best. Good luck.

Good suggestions. I've got another tach that I can use to verify the in dash gauge.

I wish we had a good prop shop. I've only found one in the area and they weren't much help.

 

[AlmostFamous]

Re: Did I choose the wrong prop? 20ft Bryant w/19p

Just to close the loop. I purchased and installed New Solas Rubex 17p 4-blade aluminum prop. The difference between the 19p and the 17p is surprising. The boat will actually plane out without going WOT. holeshot is much improved. Indicated RPMs were 4300 at WOT trimmed up. 43MPH is what the speedo was saying, but I did not verify with GPS.

All in all, I'm calling it a success. Thanks to everyone who helped me figure this out! Iboats is a wealth of knowledge.