Trying to get a little more speed with tabs and hydrofoil

[jumpjets]

I have a 22' wellcraft cuddy with a 5.7 merc and alpha one. Currently, it tops out at 42mph at about 4000rpm. I'm thinking of doing some upgrades to improve speed and efficiency.

1. Smart Tabs SX: these look like they would do exactly what I wanted. They aren't expensive either. I'm super nervous about drilling into my transom though, especially below the water line. I'm also worried that once I drill into the transom, I might find wet wood. That would ruin my day. The boat is holding together just fine, and I don't want to ruin my summer by finding out I have a soggy transom.

2. Hydrofoil: These are very cheap, and I imagine that they would aid in stability and planing. The smart tab page says specifically not to install any other planing device with smart tabs installed. Does this mean I can't install a hydrofoil with smart tabs? What would happen if I did?

3. New prop: I have a 4 blade aluminum 19 pitch prop. I think if I installed a 4 blade stainless steel 17 pitch prop, that would put the boat right into the engines power band of 4200-4600rpm, instead of down at 4000rpm where it is now. It would also keep the boat from bogging so badly when I had a full load of 6 people on board.

Thoughts, recommendations?

 

[Silly Seville]

Re: Trying to get a little more speed with tabs and hydrofoil

1. Smart Tabs = good for what they were designed for, not going to make you "go faster". If you are afraid of drilling holes because you might find out you have a wet transom, you have other issues that must be worked out before you need trim tabs.

2. Hydrofoil on your boat = JUNK! Nauticus have engineers on staff for a reason, and they're right. Tabs and batwings don't play well together!

3. A three blade SS 17p prop would be fine. Sounds like you need to reduce weight on your outings. Try carrying less fuel, and limit the amount of dead weight as well, starting with the bench seat sized coolers full of ice and extra anchors if you don't plan on using them.

How efficient do you expect a Chevy 350 to be? At rated cruise rpm and rated load weight, you MIGHT see 3 mpg. Specify your running conditions: Is that 42 mph speedo or GPS? Sole operator on board or half a dozen heavies? If you are getting 42 mph GPS at maximum rated loading, you are my hero. You don't need any other upgrades because your boat is doing something nearing impossible!

 

[tpenfield]

Re: Trying to get a little more speed with tabs and hydrofoil

I have a 22' wellcraft cuddy with a 5.7 merc and alpha one. Currently, it tops out at 42mph at about 4000rpm. I'm thinking of doing some upgrades to improve speed and efficiency.

1. Smart Tabs SX: these look like they would do exactly what I wanted. They aren't expensive either. I'm super nervous about drilling into my transom though, especially below the water line. I'm also worried that once I drill into the transom, I might find wet wood. That would ruin my day. The boat is holding together just fine, and I don't want to ruin my summer by finding out I have a soggy transom.

2. Hydrofoil: These are very cheap, and I imagine that they would aid in stability and planing. The smart tab page says specifically not to install any other planing device with smart tabs installed. Does this mean I can't install a hydrofoil with smart tabs? What would happen if I did?

3. New prop: I have a 4 blade aluminum 19 pitch prop. I think if I installed a 4 blade stainless steel 17 pitch prop, that would put the boat right into the engines power band of 4200-4600rpm, instead of down at 4000rpm where it is now. It would also keep the boat from bogging so badly when I had a full load of 6 people on board.

Thoughts, recommendations?

Actually, if you went with a 3 blade stainless steel prop, you would probably get the higher speed (45 mph +/- ?). All that other stuff is not going to give you a better top end. The 4 blade prop actually takes a few MPH off the top end. . . the aluminum prop isn't helping either . . . Try a Mirage Plus 19P

trim tabs are nice, but I do not think it is going to do much on the top end either, just better planing speed and coming up on plane, etc. A hydrofoil, may add drag on the top end as well.

 

[TilliamWe]

Re: Trying to get a little more speed with tabs and hydrofoil

My thoughts are that you are over-propped right now, or your engine isn't producing full power. 4000rpms at WOT is too low, as you already realize. You need to get propped correctly before you go adding anything else.
One step at a time.
Oh, and you can pretty much forget the hydrofoil. They may work okay on underpowered boats, or ones with weird weight issues. But your boat is not underpowered.

 

[Philster]

Re: Trying to get a little more speed with tabs and hydrofoil

If the prop did well before and over the years (engine got to max RPM range) and the engine now won't get into the max RPM range, then likely one of two things has happened:

1) the boat is water logged, and this is completely possible given the year/make/size of the boat.

OR

2) the engine is tired

Also, you are trimming up when on plane -- correct? If the drive/prop are buried, she won't get to max RPM and you'll lug the engine. Problem solved by trimming up.

Either 1 or 2 can be masked by dropping down in pitch. Best top speed will be a maximum bow lifter prop with some cupping on the edge. Mirage Plus is a decent example w/ 3 blades; just step down in pitch from your current prop, if that prop is just wrong for a non-waterlogged hull with a good engine.

If the boat's history is uncertain, you would be best to ensure the engine and hull are in good order, or you'll risk pursuing fixes to mask an underlying problem.

 

[jumpjets]

Re: Trying to get a little more speed with tabs and hydrofoil

1. Smart Tabs = good for what they were designed for, not going to make you "go faster". If you are afraid of drilling holes because you might find out you have a wet transom, you have other issues that must be worked out before you need trim tabs.

2. Hydrofoil on your boat = JUNK! Nauticus have engineers on staff for a reason, and they're right. Tabs and batwings don't play well together!

3. A three blade SS 17p prop would be fine. Sounds like you need to reduce weight on your outings. Try carrying less fuel, and limit the amount of dead weight as well, starting with the bench seat sized coolers full of ice and extra anchors if you don't plan on using them.

How efficient do you expect a Chevy 350 to be? At rated cruise rpm and rated load weight, you MIGHT see 3 mpg. Specify your running conditions: Is that 42 mph speedo or GPS? Sole operator on board or half a dozen heavies? If you are getting 42 mph GPS at maximum rated loading, you are my hero. You don't need any other upgrades because your boat is doing something nearing impossible!

I got 42 mph with 2 adults, 1/4 tank of fuel, and a medium amount of junk on board. I'd guess 100lbs of junk if you count the spare anchor, head, drinks, fishing gear, etc..

I did the speed reading using an iPhone 3G. Not pitot, not GPS, but really just cell tower triangulation.

Actually, if you went with a 3 blade stainless steel prop, you would probably get the higher speed (45 mph +/- ?). All that other stuff is not going to give you a better top end. The 4 blade prop actually takes a few MPH off the top end. . . the aluminum prop isn't helping either . . . Try a Mirage Plus 19P

trim tabs are nice, but I do not think it is going to do much on the top end either, just better planing speed and coming up on plane, etc. A hydrofoil, may add drag on the top end as well.

I never would have guessed that a 3 blade prop would be better for top speed. I'll look into a mirage with 17 pitch. I think the tabs will help with fuel mileage and lower planing speed, vice top speed.

If the prop did well before and over the years (engine got to max RPM range) and the engine now won't get into the max RPM range, then likely one of two things has happened:

1) the boat is water logged, and this is completely possible given the year/make/size of the boat.

OR

2) the engine is tired

Also, you are trimming up when on plane -- correct? If the drive/prop are buried, she won't get to max RPM and you'll lug the engine. Problem solved by trimming up.

Either 1 or 2 can be masked by dropping down in pitch. Best top speed will be a maximum bow lifter prop with some cupping on the edge. Mirage Plus is a decent example w/ 3 blades; just step down in pitch from your current prop, if that prop is just wrong for a non-waterlogged hull with a good engine.

If the boat's history is uncertain, you would be best to ensure the engine and hull are in good order, or you'll risk pursuing fixes to mask an underlying problem.

I just bought the boat last year and know squat about it's history. It had a soft spot in the deck when I bought it, and I did a localized patch job of the left rear 1/4 of the deck, and I put in new stringers in that area as well. Is the rest of the boat waterlogged? I don't know! How do i test for something like that?

I guess I'll go weigh the boat, and if it weighs 5000lbs vice the advertised 3300, I'll know it's logged. Is there an easier way to test it?

I recently did a compression test on the engine, and it was rock solid. I have no idea how old the engine is, or how many hours are on it. It has good compression, it doesn't overheat, It seems to well on fuel mileage, and it starts every time I turn the key. It has a clean bill of health IMHO.

I don't have a trim gauge, but I trim the drive when I'm on a plane, and I can usually find a sweet spot of about 2-3 extra mph.

Thanks for all the replies so far. I'll drop the batwing idea, and look into 3 bladed props.

 

[Philster]

Re: Trying to get a little more speed with tabs and hydrofoil

I'm going with my hypothesis that you are lugging around a boat full of waterlogged foam and maybe even a wet core. You addressed one area of the boat, but I'd wager the rest is just saturated and killing performance via sheer weight and more wetted hull on plane (engine has more weight to push and more hull sits in the water = more resistance).

Changing prop size would be masking the underlying problem.

Other structural experts can suggest techniques to investigate the rest of the boat's innards.

Also, should the problem be tackled (major project) you'd need to fix the underlying cause of water intrusion, which could very well be the deck/hull joint.

 

[QC]

Re: Trying to get a little more speed with tabs and hydrofoil

A few things to add here:

1) It looks like your numbers are right. Works out to 14% slip and I think that is consistent with where you are. Optimization will help some.

2) A 1990 5.7 is the old standard "260". One thing to remember though, that was rated at the crankshaft and today it would be called a 230.

3) I don't initially see a response to the trim question. You should see a significant speed increase from full down (in) to full up (out). If you are not seeing at least 5 MPH. and if you can't get her to porpoise, then I would look into shifting weight aft.

4) If you cannot get her to porpoise, trim tabs will not do much. I am a huge fan of trim tabs, for a variety of reasons, but the only real way they increase speed in a 40+ MPH boat is to control porpoise. Almost all boats are fastest with the bow up, trim tabs actually fight this, but can help if they allow the bow to be higher before she starts to porpoise. If you can't porpoise now, then you can't use the tabs to control much . . . Shifting weight aft and trim are how you get the bow up, but then she might porpoise, then you need the tabs. Definitely ask for clarity if this doesn't make sense to you.

5) If she doesn't increase to 4400+ RPM with some trim etc. then definitely a 17. Pretty scary that a 15 might even be in play which leads me to question overall weight like the others.

 

[Maclin]

Re: Trying to get a little more speed with tabs and hydrofoil

Phil, Do 22 footers have foam flotation? I am pretty sure mine does not, just asking, thought flotation was only required and present in the smaller boats.

 

[Maclin]

Re: Trying to get a little more speed with tabs and hydrofoil

I think your 4000rpm is low, especially with a 19p prop.

My boat is a 22 foot Cuddy cabin. I can get 45+ at 4400-4500rpm from my 5.7 4bbl with approximately a 23 pitch (B5) propset. I got get closer to 50 with a 25 (B7) pitch propset. This is a Volvo Penta DuoProp so the pitch is approximate. This is all original 1991 model stuff. I would not consider it an over-achiever.

Going down in pitch from 19 is masking the problem in my opinion.

 

[QC]

Re: Trying to get a little more speed with tabs and hydrofoil

Phil, Do 22 footers have foam flotation? I am pretty sure mine does not, just asking, thought flotation was only required and present in the smaller boats.

Legally, less than 20 ft.

 

[TilliamWe]

Re: Trying to get a little more speed with tabs and hydrofoil

I'm going with my hypothesis that you are lugging around a boat full of waterlogged foam and maybe even a wet core. You addressed one area of the boat, but I'd wager the rest is just saturated and killing performance via sheer weight and more wetted hull on plane (engine has more weight to push and more hull sits in the water = more resistance).

Changing prop size would be masking the underlying problem.

Other structural experts can suggest techniques to investigate the rest of the boat's innards.

Also, should the problem be tackled (major project) you'd need to fix the underlying cause of water intrusion, which could very well be the deck/hull joint.

I fear Phil is spot on with this response, jumpjet. You have some investigating to do.

Maybe a trip over to the "Boat Restoration" section will give you ideas how to check for water and where to get started?

 

[jumpjets]

Re: Trying to get a little more speed with tabs and hydrofoil

Well.....

Thanks for all the responses guys. The previous owner had a 23 pitch SS 3 blade prop installed when I bought the boat, and he said he could hit 55mph. I think he was exaggerating a little, but that is still higher than what I get.

I spent most of last winter browsing the restoration section for tips on how to do deck work. I guess I'll head back in there. It does make sense that the boat is heavier than usual. It's been shrink wrapped all winter, so maybe when I pull it out of storage, it'll have some soft spots or something that will be a dead giveaway.

Oh well, it still floats, so I'm gonna enjoy it this summer.

 

[jumpjets]

Re: Trying to get a little more speed with tabs and hydrofoil

No need to rip up the deck, just take the boat to a truck scale and weigh it. (Weight the boat, trailer and tow vehicle, launch the boat and weigh the trailer and tow vehicle and then do the math.)

That is a great idea! I'll do that as soon as I get the boat out of storage. I'll pull the anchors and misc junk out of the boat, and weigh it with an empty fuel tank. Then I'll launch it and weigh my tow rig again. Hopefully the difference will be in the realm on 3300-3500lbs.

How much water will a water logged boat hold? Will it be 100-200lbs, or something much greater?

This is gonna be on my mind constantly until I have an opportunity to test it out. Only 4 more weeks until I get home from Afghanistan. My wife is gonna be pissed that the first thing I'll want to do is tinker with my old boat.

 

[TilliamWe]

Re: Trying to get a little more speed with tabs and hydrofoil

How much water will a water logged boat hold? Will it be 100-200lbs, or something much greater? .

Depends on how much water is in there. Water weighs 8.6lbs per gallon, so it doesn't take a lot to add up. WHERE the water is at can be just as important. And while weighing it won't tell you that, it is the place to start.

If the weight doesn't reveal anything, start borrowing props and experimenting to see what gets you to your proper WOT RPMs.

 

[Philster]

Re: Trying to get a little more speed with tabs and hydrofoil

It's a 3300 lb (dry weight) boat with 260 HP.

If she were a 60+ MPH boat, I'd guess she'd be wearing a 23p, 3-blade SS prop out of the factory. I don't think that's a 60 MPH boat by any means.

If she were a 50 MPH boat, I'd guess she'd be wearing a 21p, 3-blade SS prop out of the factory. I do think that's a 50 MPH boat, give or take a few MPH. If me instincts is wrong, I'll lick the 19p prop she might have been wearin' out of the factory to hit 45+. However, this is the bottom of the acceptable prop pitch range I can imagine.

We are now talking about going down to a 17p prop?! Yikes! Get yer calcs out, boys 'n' girls, because that screams trouble to me.

 

[QC]

Re: Trying to get a little more speed with tabs and hydrofoil

I think we all sort of agree, Phil. Frankly this is like many we see here: no reliable history, so hard to follow typical troubleshooting guidelines. This could be fuel, engine condition, weight, pitch, trim, bad data or even bad karma. I am with you though that this really seems like a 21 inch application. The RPM is definitely too low, but the problem is that does not necessarily mean pitch. I say the numbers are right because they add up. I do NOT mean that 4000 RPM WOT is acceptable. It isn't

 

[Philster]

Re: Trying to get a little more speed with tabs and hydrofoil

I would love to see this boat get weighed.

 

[Tahorover]

Re: Trying to get a little more speed with tabs and hydrofoil

Depends on how much water is in there. Water weighs 8.6lbs per gallon, so it doesn't take a lot to add up. WHERE the water is at can be just as important. And while weighing it won't tell you that, it is the place to start.

If the weight doesn't reveal anything, start borrowing props and experimenting to see what gets you to your proper WOT RPMs.

Sorry it's 8.34 lbs/gallon

 

[bruceb58]

Re: Trying to get a little more speed with tabs and hydrofoil

I am betting he doesn't have foam in that boat.

With a boat that size, I would not get smart tabs. If you really think you need tabs, get helm adjustable ones.

A 19" 3 blade prop should be what he needs assuming the engine is in good shape. I personally, would make sure a tune up was done and fuel filters replaced before anything else was done.

So what were the compression numbers? You said "rock solid" but I would be interested in what you measured.