Staying On Plane at Lower Speed?

[JoLin]

Here's the scoop. The boat in my sig weighs between 8500 and 9000 lbs. with a normal load. Current props are V-P 3-blade aluminum, 19P. WOT rpm for my current rig is 4600, which puts it smack in the middle of the V-P recommended range (4400-4800). Attitude is good- she planes out pretty level.

I can stay on plane down to 20-21 mph @ 3200 rpm (pretty normal for this type of boat), but would like to be able to get down into the high teens for a couple reasons. 1. The bay can get pretty rough and I'd like to slow it down when I need to, and 2. I'm often in 'convoy' with bigger boats that cruise at 18 mph. That results in constant on plane, off plane cruising (a real PITA).

I'm thinking a 'total lift' prop like the Stiletto Bay Pro III 4-blade stainless might give me what I'm looking for. Thoughts or alternative suggestions?

 

[Bondo]

Re: Staying On Plane at Lower Speed?

Here's the scoop. The boat in my sig weighs between 8500 and 9000 lbs. with a normal load. Current props are V-P 3-blade aluminum, 19P. WOT rpm for my current rig is 4600, which puts it smack in the middle of the V-P recommended range (4400-4800). Attitude is good- she planes out pretty level.

I can stay on plane down to 20-21 mph @ 3200 rpm (pretty normal for this type of boat), but would like to be able to get down into the high teens for a couple reasons. 1. The bay can get pretty rough and I'd like to slow it down when I need to, and 2. I'm often in 'convoy' with bigger boats that cruise at 18 mph. That results in constant on plane, off plane cruising (a real PITA).

I'm thinking a 'total lift' prop like the Stiletto Bay Pro III 4-blade stainless might give me what I'm looking for. Thoughts or alternative suggestions?

Ayuh,... I may be wrong, but I believe yer tryin' to defy natural Physics...

The Hull has to get to a certain speed to plane...

 

[Philster]

Re: Staying On Plane at Lower Speed?

I have been in message board battles over this, but planing is climbing one's bow wave and staying on top of it. Others don't get this.

Some people push the nose down with tabs and they move weight around to flatten the ride below planing speeds and then call this planing, but it's actually making the boat a displacement hull.

Maybe.... just maybe you could make the tiniest little difference by keeping the boat as light as possible. That's about the only practical change you can make.

What types of boats are your cruising with? I mean, if they have trawlers and/or other non-planing or semi-planing hulls, you just have to come down to their non-planing world.

 

[chriscraft254]

Re: Staying On Plane at Lower Speed?

Does your boat have trim tabs?

 

[Texasmark]

Re: Staying On Plane at Lower Speed?

I personally have been able to "control" my boat with prop pitch. I have 4 props for my current boat: 17P, 2ea 21's, and a 24. I can set the boat to run wherever I want with the 17; running with the water just leaving the transom (the start of the plane out) if I choose. If I go to the 24, it will load up the engine and it's rock-a-bye-baby back and forth on and off plane and all that.

Other thing is trim. Tucking the engine in forces the bow down and in essence flattens out the bow wave Philly talked about and in doing so, the trim of the boat is more horizontal. Many times I wanted to just cruise around and would cut the throttle to put the boat speed below 25 mph and in the process, tuck the engine all the way in. The wake is almost flat and even with the 24P prop, I can do a very good job of controlling the boat's attitude.

You could stand some more rpm's and that says a lower pitched prop, 2" is a good number for your rpm's which will help you to control your "attitude" as I mentioned along with trim if you have it. Others have said that 4 blade props help do what you want done. I have had others say that smart tabs help to hold the stern up hence lower planing speed and actually they do alter the planing area, are mounted even with the engine and thus can help your problem.

So personally, I'd drop the prop 2" with the same brand/style prop and add smart tabs and tuck in the trim. That ought to work for you.

My opinion and you asked for it.

Mark

 

[Maclin]

Re: Staying On Plane at Lower Speed?

That is a big boat so if it does not have hydraulic tabs on it now then look into those. I am not sure of your budget and how serious you are about getting to your goal, but a conversion to DuoProp if possible would be a big improvement.

 

[JoLin]

Re: Staying On Plane at Lower Speed?

Does your boat have trim tabs?

Yes- I have Bennetts and know how to use the tabs and outdrive trim. As for dropping pitch and keeping the same type of prop, I don't think I want to go in that direction. Engine is already running in the 'sweet spot' and I don't want to upset that balance. I'll probably just live with what I have.

Thanks, all.

 

[JoLin]

Re: Staying On Plane at Lower Speed?

What types of boats are your cruising with? I mean, if they have trawlers and/or other non-planing or semi-planing hulls, you just have to come down to their non-planing world.

Not trawlers. Flybridge cruisers, mainly- Trojan 38, Silverton 34, etc. When Lin and I are trying somewhere new, we often use 'stern light navigation' to get there, since these friends are long-time boaters who know all the tricky areas.

 

[chriscraft254]

Re: Staying On Plane at Lower Speed?

Not trawlers. Flybridge cruisers, mainly- Trojan 38, Silverton 34, etc. When Lin and I are trying somewhere new, we often use 'stern light navigation' to get there, since these friends are long-time boaters who know all the tricky areas.

Get yourself a Broadband radar and you can follow them anywhere you want even without lights.

 

[dazk14]

Re: Staying On Plane at Lower Speed?

Here's the scoop. The boat in my sig weighs between 8500 and 9000 lbs. with a normal load. Current props are V-P 3-blade aluminum, 19P. WOT rpm for my current rig is 4600, which puts it smack in the middle of the V-P recommended range (4400-4800). Attitude is good- she planes out pretty level.

I can stay on plane down to 20-21 mph @ 3200 rpm (pretty normal for this type of boat), but would like to be able to get down into the high teens for a couple reasons. 1. The bay can get pretty rough and I'd like to slow it down when I need to, and 2. I'm often in 'convoy' with bigger boats that cruise at 18 mph. That results in constant on plane, off plane cruising (a real PITA).

I'm thinking a 'total lift' prop like the Stiletto Bay Pro III 4-blade stainless might give me what I'm looking for. Thoughts or alternative suggestions?

You are absolutely looking in the right direction. If you are planing at 21 with a 3 blade, it WILL plane efficiently at a slightly lower speed with a 4 blade. Sure, the 4 blade will bleed of bow lift for the sake of stern lift - but that's exactly what you want.

You want to stop driving the stern deeper(2 or 3 blade), which creates a bigger hill to climb.

Yes, we have set these up numerous times and yes, some of the boats have floscans indicating fuel usage.

In rough waters, being able to go slower can make it a MUCH more comfortable ride for passengers and we have set up many for just that reason. It's embarrassing for most owners taking out guests, that the passengers need to hold a rail instead of a drink, because they're pounding during the journey.

Watersports with small kids is another area where people request slower planing speeds. 20mph is simply not safe for small kids(including tubing). Big tabs and 4 blades are a must and 18 is doable with your application.

What size tabs are you running? For a 4 blade, you must drop a minimum of 1", but your VP prop (we sell Mercruiser) might require(likely) a 2" drop if moving to SS and a more sophisticated blade geometry.

I think I would start with a $107 Solas Amita 17" 4 blade - no hub kit needed...but there are other starting points and it wouldn't hurt to look for data on your VP prop.

This is a start anyways...

 

[CaptainKickback]

Re: Staying On Plane at Lower Speed?

Once you get the boat to running on plane at the slowest speed that you can, if that's not slow enough, ask your friends to kick it up a couple of knots. Just because they typically cruise at 18, doesn't mean they can't do a little more. I know they are watching their fuel flow, but heck, their friends, right?

Good luck...

 

[JoLin]

Re: Staying On Plane at Lower Speed?

Once you get the boat to running on plane at the slowest speed that you can, if that's not slow enough, ask your friends to kick it up a couple of knots. Just because they typically cruise at 18, doesn't mean they can't do a little more. I know they are watching their fuel flow, but heck, their friends, right?
Good luck...

Big difference in fuel usage when you're running a pair of big blocks in a 38' Trojan. I don't blame them a bit for wanting to run at their own most efficient speed. I'm just the little guy with a pair of sixes.

Chriscraft254, I eagerly await your contribution toward my new radar. Oh- I'll need an arch, too. Thanks. You're the best!

dazk14, thanks for the advice. I didn't think I was totally out of line, as I based my question on my own experience with a butt-heavy 21' Pro-Line (175 hp outboard on a 36" setback). After a ton of research I replaced the 3-blade, 19P aluminum 'whatever' prop for a Solas Titan HR- 17P 4-blade stainless. The difference was pretty dramatic.

I know my Four Winns isn't really unbalanced, but I thought I might gain some advantage from the Stiletto, which is billed as a 'total lift' prop, where the Titan (or a Bay Pro II) was specifically designed to provide stern lift. The Titan definitely did what it claimed, so why not the Stiletto?

Anyway, I'll give it some thought and take a good look at the Amita. It's certainly a lot cheaper than the Bay Pro III.

Thanks again, all. As usual, good stuff to think about.

 

[bnicov]

Re: Staying On Plane at Lower Speed?

Why not try a pair of 4 blade 17p. You'll still be in the sweet spot with regards to rpms but you'll plane quicker and at a slower speed.