Solutions to excessive planing speed

[CChase86]

I spent some time looking around on the forums but didn't find the answer I was looking for. I've got a 1995 Four Winns 170 Freedom with a 4.3GL/Volvo SX I/O.

My issue is that the boat requires what I consider to be an excessively high planing speed of about 22-24 mph or so, at which it porpoises occasionally despite my best efforts at trimming it and moving weight around in the boat.

I'm kind of opposed to the concept of a hydrofoil as I feel it's a band-aid fix to the problem and might do more harm than good anyway. I have been reading about smart tabs and other trim tab type options, but I'm not sure where they go on a hull design like mine where the I/O is not on a flat transom but set in about 18" or so.

What are my best options for lowering the cruising speed on plane and helping to reduce or eliminate the porpoising?

Thanks in advance.

EDIT: Here is a picture of the back of the boat (not my personal boat) http://www.bobsbeaconmarina.com/catalog/images/boston09 098.jpg

 

[Bob_VT]

Re: Solutions to excessive planing speed

I would check to see if you have water logged foam and it is changing the balance.

 

[Bob_VT]

Re: Solutions to excessive planing speed

Is this a new problem or has it always been that way? Have you changed the prop this year? Based on your statement "porpoises occasionally" I am concerned with the weight.

I just noticed Newport !! Hello fellow Vermonter

 

[blouderback]

Re: Solutions to excessive planing speed

Do some research on Smart Tabs (tm). There's no wiring needed, and they automatically adjust themselves at different speeds and conditions. I have never tried them, but I've never heard anyone report bad experiences with them either.

 

[MikDee]

Re: Solutions to excessive planing speed

The extension of the hull past the transom (outdrive), we used to call "squattin boards" (trim tabs) on a hydroplane, this is made to keep the bow down, help it get on plane, and keep it from porposing. So, it actually has built in trim tabs already. I would think if you are trimming up at speed, you're going against the force of the extended hull design, and just compounding the planing, & porposing problem, at least that's what I found when I had my hydroplane. I don't think trim tabs will help you, it will just make it worse. That hull design doesn't respond well to Any trimming. By the way, losing 1-1/2' from a 17' boat, moves the engine weight further forward complicating things even more. Try keeping your trim all the way down when using the boat, and see if it responds any better.

 

[CChase86]

Re: Solutions to excessive planing speed

Is this a new problem or has it always been that way? Have you changed the prop this year? Based on your statement "porpoises occasionally" I am concerned with the weight.

I just noticed Newport !! Hello fellow Vermonter

Hi,

The problem has always been this way. The previous owner installed a hydrofoil to help keep this from happening but I wanted to avoid hydrofoils so I took it off when I bought the boat. No prop change, has the stock propeller on it.

The extension of the hull past the transom (outdrive), we used to call "squattin boards" (trim tabs) on a hydroplane, this is made to keep the bow down, help it get on plane, and keep it from porposing. So, it actually has built in trim tabs already. I would think if you are trimming up at speed, you're going against the force of the extended hull design, and just compounding the planing, & porposing problem, at least that's what I found when I had my hydroplane. I don't think trim tabs will help you, it will just make it worse. That hull design doesn't respond well to Any trimming. By the way, losing 1-1/2' from a 17' boat, moves the engine weight further forward complicating things even more. Try keeping your trim all the way down when using the boat, and see if it responds any better.

Interesting, this is what I assumed the design was for although apparently it's not too successful. I'll try keeping the trim all the way down but I am guessing the plane speed is still going to be fast.

I would check to see if you have water logged foam and it is changing the balance.

I thought of this but the foam is dry.




So it seems that trim tabs won't help and I might just be stuck with the high cruising speed unless I want to stick a hydrofoil on.

Are there different props I could get that would help lift the back of the boat up or any other options?

 

[MikDee]

Re: Solutions to excessive planing speed

I understand your angst, this boat was designed with built in 18" trim tabs, it can be a blessing, or a curse, depending on water conditions. Extending the transom out another 8-10" with tabs is absurd, having so much wetted surface past the prop, can really be a drag, especially if you try to trim up, it affects power, & fuel efficiency. It would probably be less of an issue with a lighter 4cyl motor because it's a rather small boat 17'. Have you tried the hydrofoil?
I usually recommend Smart tabs, but in this case I suggest a hydrofoil, and my choice is a Doel fin style, because it is the least intrusive (smallest), First, & oldest, proven effective hydrofoil design, that all others have copied, and some have gotten outlandish with (IMO).

Being the cheapskate I am, I've had a hydrofoil on most of my boats, and been very happy with the results. I never even heard of Smart tabs till I got to this site.

By the way, just a thought here, a hydrofoil works even with the trim down

 

[CChase86]

Re: Solutions to excessive planing speed

I guess my concern with the hydrofoil is (and correct me if I am misguided) that it "has" to add a significant amount of drag to the boat. When it makes a difference to wax a hull over a dull finish I can't believe that adding a wing to the back of the boat would help it out.

I know there are many claims that hydrofoils don't affect top end speed or fuel consumption but I'm skeptical at best. I have a Stingray hydrofoil that was on the boat when I got it, it's been sitting in the basement since then. I could put it on and try it out but I'm just very skeptical at this point.

Thanks for the insight/help/advice so far.

 

[MikDee]

Re: Solutions to excessive planing speed

I guess my concern with the hydrofoil is (and correct me if I am misguided) that it "has" to add a significant amount of drag to the boat. When it makes a difference to wax a hull over a dull finish I can't believe that adding a wing to the back of the boat would help it out.

I know there are many claims that hydrofoils don't affect top end speed or fuel consumption but I'm skeptical at best. I have a Stingray hydrofoil that was on the boat when I got it, it's been sitting in the basement since then. I could put it on and try it out but I'm just very skeptical at this point.

Thanks for the insight/help/advice so far.

I think a hydrofoil is the lesser of all evils in your case. When you get on plane with your boat, then try to trim up for speed, those two sponsons on the back angle down, & create drag as it is, can you imagine what extra trim tabs would do? a Hydrofoil is the least of your drag at any time. I just noticed another issue, is there enough room in between the setback for a hydrofoil, with out hitting either side when trimmed up? (like when beaching?).

By the way, what size, & type of prop do you have?

 

[CChase86]

Re: Solutions to excessive planing speed

Good point. There is adequate clearance for the hydrofoil that was on there for it to move around in all dimensions.

To clarify on my original post, I never said I "wanted" trim tabs, I just wondered where they would even go as I ventured to guess that the design of the transom was supposed to act as an integrated trim tab.

The prop that is on there is the stock propeller for the boat, it's a 3 bladed unit listed as 14.25" diameter x 21" pitch.

 

[RotaryRacer]

Re: Solutions to excessive planing speed

You need to look at the prop. That boat should hop on plane with no bow rise and no porpoising. The hull design is pretty highly acclaimed for being stable at all speeds and giving good hole shot performance.

Tell us about the prop and your WOT speeds and RPMS. I'd guess the boat is overpropped. If you went down in pitch I would bet the boat would perform better overall. If the current prop is damaged it could also be contributing to these issues.

 

[CChase86]

Re: Solutions to excessive planing speed

You need to look at the prop. That boat should hop on plane with no bow rise and no porpoising. The hull design is pretty highly acclaimed for being stable at all speeds and giving good hole shot performance.

Tell us about the prop and your WOT speeds and RPMS. I'd guess the boat is overpropped. If you went down in pitch I would bet the boat would perform better overall. If the current prop is damaged it could also be contributing to these issues.

Sorry, I think I worded it wrong. The boat doesn't have a problem getting onto a plane, it just requires that you're going about 22 mph to stay up on it. Although if what you say is true and that it should be stable at a wide range of speeds it sounds like something is up.

I mentioned above (at the same time you posted) that the prop is stock, 3 blade, 14.25" diameter 21" pitch aluminum propeller.

Off the top of my head I don't remember what WOT RPM's or speed are but I believe with about 3/4 tank of gas and 400 lbs of cargo it was doing about 41 mph or so. I'll be able to report back with more specific speed/RPM information after this weekend hopefully.

EDIT: 400 lbs is cargo AND people, should have been more specific.

 

[MikDee]

Re: Solutions to excessive planing speed

You need to look at the prop. That boat should hop on plane with no bow rise and no porpoising. The hull design is pretty highly acclaimed for being stable at all speeds and giving good hole shot performance.

Tell us about the prop and your WOT speeds and RPMS. I'd guess the boat is overpropped. If you went down in pitch I would bet the boat would perform better overall. If the current prop is damaged it could also be contributing to these issues.

IMO, A 17' boat with a 4.3V6 in it, I think a 21" pitch prop is not overpropped, it is just right! but, of course this info might help.

 

[tashasdaddy]

Re: Solutions to excessive planing speed

i despise hydrofoils, great for small motors, 25 and below. spend $99.00 on a set of blemished Smart Tabs, and get the take TAIL HEAVY boat on plane, and keep it on plane longer.

this is your solution. http://www.iboats.com/Factory_Blemi...z.54646--**********.128148999--view_id.486633

http://forums.iboats.com/showthread.php?t=313041

 

[RotaryRacer]

Re: Solutions to excessive planing speed

CChase's post on the prop pitch happened while I was typing my post. I agree a 21" pitch prop doesn't seem to far out of line. However, I think that this boat should be staying on plane at a lower speed and a lower pitch may help in that regard.

I don't think smart tabs will be able to be installed on this boat.

This isn't the exact model however the basic transom/afterpod design is the same.

 

[Bondo]

Re: Solutions to excessive planing speed

i despise hydrofoils, great for small motors, 25 and below. spend $99.00 on a set of blemished Smart Tabs, and get the take TAIL HEAVY boat on plane, and keep it on plane longer.

this is your solution. http://www.iboats.com/Factory_Blemi...z.54646--**********.128148999--view_id.486633

http://forums.iboats.com/showthread.php?t=313041

Ayuh,... I completely Agree,... There's Plenty of space on the transom for them,...
I'd go with Smart Tabs, Long before I put a Fin on the drive...
The drive is built for Pushin',... Not Lifting the boat...

 

[180shabah]

Re: Solutions to excessive planing speed

Lets back up and hit the basics first.

Agreed - check the weight and compare it to manufacturer specs.

Next verify the running surface - from the transom forward the first 4-5 feet should be straight and flat. Any hook(concave) or rocker(convex) will drastically affect performance.

 

[CChase86]

Re: Solutions to excessive planing speed

I don't really have a method to check the weight of the boat but I really don't think it's the issue, if the weight was that far off that it was affecting the ability of the boat to stay on plane I feel like it would be hard to get on plane, be sluggish, get poor fuel economy, sit in the water lower, etc. It's also not stored in the water and the foam (from what I can tell) is dry.

I'm starting to get lost in all the suggestions here, some of which are conflicting.

I think I'm going to have to take the boat out, re-evaluate everything, and then report back with a clearer picture. I'll also have to take some detailed pictures of the hull design.

 

[Varago]

Re: Solutions to excessive planing speed

Just a thought but are you sure your doing 22mph is it with a GPS or speedo? The speedo in my boat is soooo bad it reads 23 at 19.

Dave

 

[grego]

Re: Solutions to excessive planing speed

Put hydros back on. go to lowes and get a few bags of play sand and move them around on boat to get the right cg. "center of gravity". Wetjets were really bad about porposing, now they have bladder that can be filled in nose of jet to fix problem. If outboard, 'jack plate'! A LOT depends on swell or wave conditions.