Ken2 Prop Question

[CaptnC]

Ken,

You were very helpful on the thread "over there" and would like to ask you:

I know you are not a big fan of 16" Suzuki props, but what kind of gain might I possibly see going to a 16X21.5?

I currently have the 14 3/4X23. I have the engine at the proper height per you on the other thread. I am currently getting 6000rpms while making 45knots...trimmed high and WOT...

4200rpms=25knots=2.8mpg

?rpms=29knots=2.0mpg

6000rpm=45knots=?mpg

Full load of fuel (166 gallons) and three average adults (200lbers) safety gear and thats all.

The prop don't bite very well from a medium/heavy throttle, hole shot, at a normal cruise trim. If I trim down some (not all the way) I have no problems.

What if any improvments could I see? Less slip during hole shot? Better speed and econmy?

I'm pretty pleased with numbers I am getting, but want to be sure I am getting everything I can out of the DF175's I have on the boat (1999 25' SeaCraft).

[triumphrick]

Just an observation....those are some killer mpg #'s for that boat and with twins!! Definitely doing something right. Must be the Zukes.....

[ken2]

I agree with triumph, Those numbers are very good.

Your rpm is Perfect.

Staying with the same style prop, and just going down in pitch isn't going to change much. It will accelerate better, but its going to cruise slower and not as efficient, and probably not be as fast on top end either. Its still going to ventilate when you trim them up.

I would get a good prop shop to put a little cup into your existing ones.

It will lower your rpm by about 150-200 which is fine, you'd still be ok at 5800 or 5900 rpm.

The cup should help with the slip or ventilation your having. Should bite better throughout the rpm range. You'll still get your good economy, heck you may even improve on it.

It doesn't cost much either. probably about 60-70 bucks for the set.

There have been quite a few guys that had ventilation issues with those props, and lots of them liked 4 blades for the better bite, but as good as your numbers are, I'd spend $60-70 try a little cup before you try a different set.

[CaptnC]

I agree with triumph, Those numbers are very good.

Your rpm is Perfect.

Staying with the same style prop, and just going down in pitch isn't going to change much. It will accelerate better, but its going to cruise slower and not as efficient, and probably not be as fast on top end either. Its still going to ventilate when you trim them up.

I would get a good prop shop to put a little cup into your existing ones.

It will lower your rpm by about 150-200 which is fine, you'd still be ok at 5800 or 5900 rpm.

The cup should help with the slip or ventilation your having. Should bite better throughout the rpm range. You'll still get your good economy, heck you may even improve on it.

It doesn't cost much either. probably about 60-70 bucks for the set.

There have been quite a few guys that had ventilation issues with those props, and lots of them liked 4 blades for the better bite, but as good as your numbers are, I'd spend $60-70 try a little cup before you try a different set.

Thanks guys!

I have been chatting with a guy who has 27 Contender that is claiming better top speed (50knots) and cruising at 30knots getting 2mpg w/ a full load. And yes his claims are in knots too, not MPH.

He has the 16X21.5 Suzuki props...that is why I thought they might be worth trying. I'm not sure which 27 Contender he has...seems some older 27'ers are 27' long and newer ones are 30'. I don't know much about the brand other than they build a great boat. Any way I think his is the older 27...

Ken I know you're not going to like this...but I installed the SE Sport 300 Hydrofoils on the motors...I have to deal with head seas almost every trip out which causes me to have to run at slower speeds to keep from beating everyone to death. I'm not sure that these engines will be able to keep the boat on plane at the slower speed (20knots and less at times). I feel heavy tabs cost me MPG (seen it on the FloScan with the Optis) and some knots. When I added the SE Sports to the Optis I planed better at slower speeds without much if any tabs. I had always used the tabs to only balance load. I was also able to cruise about 2 knots faster without any add pounding.

[ken2]

Zuke props are pitched higher then they are stamped, which makes it hard to figure out prop slip numbers or what a "realistic" top speed might be.

Your slip numbers. 6000 rpm, 2.5 gear ratio, 23 pitch, 52mph comes out to .005 slip. which is not really possible if they were truely 23 pitch.

The other guy with 21.5 pitch props. would be at a negative slip number. But who knows, maybe his boat is just set up really well.

The last 27 Contender (older) I ran had a tough time cracking 50mph with a decent load and F225's.

But loaded light is a different story.

4 blades will help keep your bow down and fix the ventilation. But I'd still cup those things and see what happens.

[CaptnC]

4 blades will help keep your bow down and fix the ventilation. But I'd still cup those things and see what happens.

Will do!

Thanks!

[PatrickG]

We've never cracked 60 with a light load on a 27 Contender and F250's. I would be extremely surprised if somebody is getting 57.5 mph on a 27 Contender with twin 175's.

[CaptnC]

I went back and re-read his message to me...his top speed was over 40 knots (42knots to be exact). So yeah, its pretty much a slam dunk I have my rig set up about as goo as it gets.

Thanks again guys for taking the time to reply.