Which Prop for Bristol 45.5?

[LAnderson]

Hi All,
I am considering a 1988 Bristol B45.5 that has a Westerbeke 70HP engine with a 3 blade max prop on a 1-1/4in diam. shaft. I would be taking it 1,300 miles on the ICW and am considering temporarily changing to a 3 blade fixed prop for that trip. Do you have any spec's on what the prop should be and where to buy a good used one? I'd use that fixed prop later as an emrgency backup also. Thank you! Andy

 

[kappykaplan]

Westerbeke 70HP engine with a 3 blade max prop on a 1-1/4in diam. shaft.

Why do you think you need to change out the MaxProp for this trip?
Welcome to the forum!

 

[dlochner]

There is no need to swap out the Max Prop. You will learn to appreciate the power it has when docking and maneuvering in close quarters. And when you can sail, you'll easily get an extra ½ to 1 knot in speed. We've done the ICW twice with a Max Prop and were frequently thankful for its power.

Do examine the prop for wear. Like all mechanical things bronze, over time the gears wear and the prop gets sloppy. PYI will service the prop and make it like brand new. Mine is headed there this winter.

 

[LAnderson]

Thanks!

99% of my ICW trip will be done under power. The fixed prop is more efficient under power than the max prop, and my surveyor recommended it and I agree. I also should have a spare anyway.

Do you have any info on the prop?

 

[dlochner]

Thanks!

99% of my ICW trip will be done under power. The fixed prop is more efficient under power than the max prop, and my surveyor recommended it and I agree. I also should have a spare anyway.

Do you have any info on the prop?

Your surveyor is wrong. The Max Prop has is awesome under power. Especially when maneuvering in tight quarters or docking. Because of the flat blade design the prop walk is strong especially in reverse. I'd spend the money somewhere else, but it is your boat and your money.

 

[PaulK]

Thanks!

99% of my ICW trip will be done under power. The fixed prop is more efficient under power than the max prop, and my surveyor recommended it and I agree. I also should have a spare anyway.

Do you have any info on the prop?

A quick internet query found this:
AI Overview
Maxprop is slightly less efficient in forward motion but has vastly superior performance in reverse and under sail compared to a fixed propeller. Under power in forward, Maxprop is only about 2–4% less efficient than a fixed propeller, a difference that can often be eliminated by proper pitch matching. However, the real advantages are its increased sailing speed and near-identical, high-efficiency reverse thrust, unlike a fixed prop which has significantly weaker reverse performance.

That is interesting information.
If you think you might need to back off a sandbar or two on your way down the ICW it would appear that the Maxprop might be worth keeping. Is 4% less efficient equivalent to having to motor into a headwind? You're not planning to wait for a tailwind before settng out every day are you? Will the cost of changing from one prop to the other (let alone the cost of the new prop) be more than the improved performance is worth?

 

[dlochner]

If you think you might need to back off a sandbar or two on your way down the ICW it would appear that the Maxprop might be worth keeping.

Absolutely! Not that I might have any experience with this.

 

[Don S/V ILLusion]

not sure I would blindly agree with your surveyor. The 0.5 knot theoretical difference isn’t as much of a concern as what’s in the water. The ICW, in parts, can have lots of floating detritus which can and often does foul a prop. A folding or feathering prop is less likely to foul. For that reason alone, I wouldn’t consider switching.

 

[LAnderson]

Thanks all, I would still like spec's for the prop as a spare.

1988 Bristol B45.5 that has a Westerbeke 70HP engine with a 3 blade max prop on a 1-1/4in diam. shaft

 

[kappykaplan]

Thanks all, I would still like spec's for the prop as a spare.

1988 Bristol B45.5 that has a Westerbeke 70HP engine with a 3 blade max prop on a 1-1/4in diam. shaft

Your local boatyard should be able to make a recommendation.

 

[dlochner]

Thanks all, I would still like spec's for the prop as a spare.

1988 Bristol B45.5 that has a Westerbeke 70HP engine with a 3 blade max prop on a 1-1/4in diam. shaft

No one here can give you a viable recommendation on pitch and size. It will be necessary to contact the prop manufacturer with the boat model, engine and HP, transmission and transmission ratio, and the distance between the center of the prop shaft to the hull after leaving the cutless bearing.

 

[FastOlson]

Posts similar to this one (and not to reflect on this poster only, and noting that the subject is a boat he/she does not even own.) seems to generally fall into the category of confirming bias and not seeking to benefit from other boaters' experiences and wisdom.
(Not that I would ever do that, of course...!)

 

[LAnderson]

Dear FastOlson,

Quick to accuse without knowledge,hmmm.

I am about to close on a boat and am preparing well ahead. That is what I do for everything, think ahead.

I had sought some friendly and helpful advice on a particular issue, the proper original prop for a particular boat.

I have been enlightened, and will now seek a friendly forum.

Sorry to have intruded.

No need to reply as I will now block from this forum.

Best of luck,

LA

 

[jssailem]

Hi @LAnderson and Welcome to SBO.

Way to often we see queries that desire information that conflicts with the cost effectiveness of the new owner based on their post.

It is your boat. You can outfit it as you see fit.

To address your question, I installed a Campbell Sailer 3 blade prop made by WestbyNorth. I have found it to be a rewarding decision. My boat is a 35ft Cal Cruiser. I would recommend the prop builder and the design for a fixed prop to push the boat at hull speed.

You need the distance from the center of the shaft to the bottom of the hull where you will locate the prop. You will also need the rotation of the shaft and the transmission ratio. The link below is used to get a quote.

Propeller Recommendation Form - West By North

Tell us about your propeller application with the form below. We will recommend a propeller based on calculations from boat speed, engine output and marine gear reduction ratios, with no hull conditions considered. Accordingly, we do not make and warranty for these estimates. If necessary, the...

westbynorth.com

Good luck with your passage.