Any Bayliner Trophy 350 V8 owners out there? Need prop size info

[treeeman00]

Hey guys, im looking for some input of Bayliner trophy 350 V8 Omc Cobra owners info. What size prop do you have on your boat? I bought my boat with no outdrive. I bought another outdrive but I think it has to small of prop. I need to know the corect prop size. Any help is greatly appreciated. Thanks.

 

[HT32BSX115]

Re: Any Bayliner Trophy 350 V8 owners out there? Need prop size info

Howdy,

This is really a prop question and we do have a Prop Forum here. Maybe a MOD will move this thread for you.

It would helpful to know a few things.

Your drive ratio, Pitch, WOT speed and RPM

Your Speed needs to be verified (GPS, etc) as does your tach. There's NO WAY to determine if a boat is running correctly if the either the speed or RPM is not accurate.


The drive should be something like 1.41:1 but without knowing the year model, it's a guess. I have a chart someplace, I'll post it if I find it.

I bought another outdrive but I think it has to small of prop

You must have some performance numbers? Speed and RPM with your current prop?

 

[jestor68]

Re: Any Bayliner Trophy 350 V8 owners out there? Need prop size info

What year, type, and size is your boat?

 

[jestor68]

Re: Any Bayliner Trophy 350 V8 owners out there? Need prop size info

You must have some performance numbers? Speed and RPM with your current prop?

He states that he bought the boat with no drive, so the best we can do is put the numbers(when we find out what boat we're talking about) through a prop selector to come up with a recommendation.

 

[treeeman00]

Re: Any Bayliner Trophy 350 V8 owners out there? Need prop size info

hey guys, sorry I posted this in the wrong section to begin with. My boat is a 1987 24ft bayliner trophy. The boat had a 305 in it originally but I repowered it with a 350 chevy. I havent had the boat out on the water yet. I was just looking to see if anyone had the same boat as I and compare props. Ill get what the curent prop size on it today. I know its a 13 something, just seemed kinda small to me.

 

[HT32BSX115]

Re: Any Bayliner Trophy 350 V8 owners out there? Need prop size info

He states that he bought the boat with no drive, so the best we can do is put the numbers(when we find out what boat we're talking about) through a prop selector to come up with a recommendation.

Yeah.....

I bought another outdrive but I think it has to small of prop.

Hmm. but he also stated that he bought another drive.

hey guys, sorry I posted this in the wrong section to begin with. My boat is a 1987 24ft bayliner trophy. The boat had a 305 in it originally but I repowered it with a 350 chevy. I havent had the boat out on the water yet. I was just looking to see if anyone had the same boat as I and compare props. Ill get what the curent prop size on it today. I know its a 13 something, just seemed kinda small to me.

Well, you're in the right section now!

You're not going to know which way to go until you run it. If you have a 13p prop on it now, it might be a little low but you NEED to know your drive ratio...You might be able to get away with a 15 but run it and see what it does.

With the correct drive ratio, prop and the engine running correctly, you should turn at the top of your recommended RPM range at Wide-Open-Throttle (WOT)

You cannot make a prop decision until you determine the drive ratio, run it and get some numbers

 

[jestor68]

Re: Any Bayliner Trophy 350 V8 owners out there? Need prop size info

Testing any prop with a "13" anywhere in the size would be a waste of time, as that is not even close to the appropriate size for this boat/motor combination.

 

[HT32BSX115]

Re: Any Bayliner Trophy 350 V8 owners out there? Need prop size info

Testing any prop with a "13" anywhere in the size would be a waste of time, as that is not even close to the appropriate size for this boat/motor combination. View attachment 183607

Well,

lessee.....prop slip calculator ran with 1.43:1, 13p, 4800(RPM), and 15% slip yields about 45mph

For any a cruiser type boat with an SBC that seems to be "in the ball park" .maybe not perfect and maybe a 15 or 17 might also work but I would start with determining what the drive ratio is before even changing the prop.

 

[treeeman00]

Re: Any Bayliner Trophy 350 V8 owners out there? Need prop size info

how do i determine the ratio? im assuming by taking the cover off and counting th teeth by the number of turns the prop makes?

 

[jestor68]

Re: Any Bayliner Trophy 350 V8 owners out there? Need prop size info

Well,

lessee.....prop slip calculator ran with 1.43:1, 13p, 4800(RPM), and 15% slip yields about 45mph

For any a cruiser type boat with an SBC that seems to be "in the ball park" .maybe not perfect and maybe a 15 or 17 might also work but I would start with determining what the drive ratio is before even changing the prop.

Interesting. The "BAM" calculator using 1.43, 13 pitch, 4800 rpm shows 41 mph theoretical and 35 mph at 15% slip.

I've run three different ratios, and come up with 17, 18, or 19 pitches.

 

[HT32BSX115]

Re: Any Bayliner Trophy 350 V8 owners out there? Need prop size info

Interesting. The "BAM" calculator using 1.43, 13 pitch, 4800 rpm shows 41 mph theoretical and 35 mph at 15% slip.

I've run three different ratios, and come up with 17, 18, or 19 pitches.

I used the same one! Prop Slip Calculator

Hmm.. Glad you did that.....

I just did it again just now and got exactly the same numbers you got! Don't know what I screwed up before !!

how do i determine the ratio? Im assuming by taking the cover off and counting th teeth by the number of turns the prop makes?

You can pull the top cover and count teeth.

I don't like to do that because you run the risk of causing a leak. It's very easy to just turn the input shaft with the drive in gear and count blades.....if the drive is in the boat, pull the plugs, and turn the engine. Have a helper either count blades or turn the engine......with the plugs out it's not all that hard.....If the drive is off the boat, it's even easier.

1.43:1 Is basically 1.43 (eng) revolutions to 1 prop revolution.

It's pretty hard to measure 1.43 revolutions so you turn the input shaft 14.3 (0.3 is about 1/3 of a turn) revolutions on the input shaft and count 10 turns of the prop (if it is indeed 1.43:1) If it's a 1.41:1 drive, then 14 input turns will be approx 10 prop turns.

If it's not, turn the input shaft 10 turns and count the prop turns. 1/3 turn (one blade of a 3 blade prop) is 0.33 revolutions. You can get pretty close. if you want to get REALLY close measure with a protractor 1 full turn is 360 degrees........ so 1/2 of a turn is 180 degrees, 1/10 of a turn is 36 degrees and so on.

Then use a hand-held calculator

2 examples below:

15 input turns and 10 prop turns= 15/10 = 1.50:1

11 input turns............ 6+ 2/3 prop turns [6 full turns and 2 additional blades] (6.66 turns) 11/6.66= 1.65:1


You do not have to be that close. the Cobras were only made in certain ratios. The ratios used with the V-8's was either 1.41: 1 or 1.43:1 With most planing, runabout (non-racing) boats you want something around 1.4--1.5:1 to give you approx the right prop RPM for most V-8's that run 4500-5000 RPM at WOT


If I lived closer, you could try my nearly new SS 17p OMC prop. It would probably be closer to what you need.

Your boat with a 17p prop would do about 45 mph or so (I think I got it right this time!!):facepalm:


Here's a chart with OMC ratios

Mine was a 1.43:1 (460 King Cobra) Yours should be a 1.41:1 ...........If you do decide to pull the top cover make sure you replace the O-ring to prevent leaks.