Spray patterns behind 18ft Chieftain

[Furrylittleotter]

I was watchings Rob's excellent video of his Prize Winning restoration and I noticed around the .52 second mark you could see a noticeable "Spray" directly behind the boat that appears to go back about 6-8ft, there are 5 or so distinct sprays and I have not seen such a pattern behind a boat. (not that I've see n that many wakes, 10 in my life maybe, but never one quite like that)

I asked Rob about it and thought I would get some more input as to 1. Is that normal for a Starcraft?, 2. For Chieftains in particular?, 3.Is it necessarily a bad thing, to be avoided, and ultimately my question would be, "If it's bad, how can I avoid it?" The lake is clear as glass so that's not the issue.

Here's the video https://www.youtube.com/watch?v=GiE2Eoh9KXg

and to be clear I think his boat and the blog he did on it are awesome and informative, I'm just curious?Since I AM building a Chieftain...

Its been awhile since I read his blog so I can't remember every detail about his setup, but as I recall, it's pretty straightforward, and he did mention he has trim tabs...

Any thoughts?


Neil

 

[Furrylittleotter]

Response from first inquiry:

Thanks for taking a look at my Chief. I do have the Nauticus smart tabs installed and I know what your taking about, you can see their tracks in the wake on each side. I've been thinking about lowering the pressure setting on the tabs to see how they perform and that would maybe create less drag. If I can get the same benefit from the lower tension strut position it would mean more speed while using less fuel.

I just watched the video again, cruising at 30 MPH the wake looks pretty much like you expect and you can see the tab tracks. It's when the boat is WOT and near 50 MPH that wake goes into spray mode as it leave the stern.

To the best of my knowledge, there isn't a topic about it currently.

IMO, that spray behind Rob's Chief is related to pushing (passing?) 50mph in a hull not designed for that type of speed, but that certainly isn't based on any actual knowledge, experience or engineering......

W/ the tabs, there's still plenty of hull in the water, even if it's up to speed and planing. Same qualifiers to my last statement....

 

[Weep'n Willy]

This is off my Chief at cruising speed.

 

[laurentide]

I think you're seeing turbulence feedback from the hull profile, but I could easily be wrong. Like jbcurt said, most aluminum hulls like ours aren't powered with that much HP and stern weight. I have an outboard, so not a perfect comparison, but my wake looks like every other OB wake I've seen. My boat could also be considered underpowered by some. The only photo I have has transducer spray before I adjusted it:

 

[Watermann]

Here's a still shot at cruising speed (32 MPH) Looks pretty normal but shows the trim tab tracks in the wake clearly. One thing I noticed is that with the tabs it flattens out the boat with more lift in the stern which allows me to trim the drive higher

 

[Furrylittleotter]

I'm learning here. Thanks for those shots, guys. The first two pictures today look about line I would expect, little if any spray.

So, what speed is the Chieftain designed to run?!

If it's under 50 I have no worries!

I have read they are made to plane around 24 knots. Is that correct? If so how would inboard vs outboard vs inboard/outboard reduce or increase the speed needed to plane?

I would think the more weight in the rear the easier they plane but I THINK I read it us just the opposite.

And how do trim tabs factor in on a Starcraft chieftain? Any increase or decrease in planing speed?

I'm hoping to plane, but I won't cry in my pillow if I can't.

Neil

 

[laurentide]

You definitely want to plane. My 18' gets up at 17 mph, with smart tabs it stays up at 14 mph in calm seas. Not sure where yours should be...it's a 25'? They're not very good displacement hulls, they plow water between hull speed and planing speed and burn tons of fuel.

I got the tabs because I don't have the luxury of picking my days. In rough water, the shallow deadrise hull pounds your brains out. With tabs you can run on plane at a lower speed, less pounding. They're worth researching if you're taking this rig offshore.

 

[Furrylittleotter]

Since it will be a diesel I'm not positive it will burn more fuel either way. Mine is 21.5ft, I think that would make it a 22footer? Good to hear you plane at such a low speed. I don't know where I read 24 knots.

I am hoping to go in Monterey Bay some and Tahoe can get choppy I hear so smoother is better in my book.

I'm not a boat guy. I'm learning. I didn't know trim tabs could make the ride smoother in chop.

I thought they just lowered the bow to allow better trimming of the lower unit(which my inboard setup will not have)

More questions.

Neil

 

[laurentide]

The "smart tabs" (that's the actual brand name) are passive. They push the bow down at lower speeds, and are level with the bottom of the hull at higher speeds, adding stability. The more expensive ones are usually Bennett's, which are actively controlled hydraulic or electric tabs that can do a lot more, like correcting list or lateral tilt. The smart tabs are great and they're cheap...active tabs are better but way more expensive.

But I'd run your boat first and see if you need/want them. They do make a difference and are an easy add-on.

 

[Watermann]

Since it will be a diesel I'm not positive it will burn more fuel either way. Mine is 21.5ft, I think that would make it a 22footer? Good to hear you plane at such a low speed. I don't know where I read 24 knots.

I am hoping to go in Monterey Bay some and Tahoe can get choppy I hear so smoother is better in my book.

I'm not a boat guy. I'm learning. I didn't know trim tabs could make the ride smoother in chop.

I thought they just lowered the bow to allow better trimming of the lower unit(which my inboard setup will not have)

More questions.

Neil

If you're plowing water at WOT traveling at say 15 mph but not achieving a plane you will consume a far greater amount of diesel fuel than if you were traveling on a plane above the water at say 20 mph which takes less throttle to maintain speed once a plane is achieved...., say your still WOT then you would have traveled 5 miles further on the same amount of fuel. It does matter big time. If the tabs make your boat obtain a plane it will go faster with the same amount of fuel being consumed.

The tabs will stabilize the boat in rough water by self adjusting to the waves and the ride ends up being smoother.

The last point is mute for your configuration.

 

[Furrylittleotter]

You bring up a couple interesting points, as far as the fuel usage, imho it is impossible to have intelligent conversations concerning fuel usage without hard data so I will get to that when I get the thing running.

In principle I agree with what you are saying but there are so many unknown factors I doubt any interesting argument can be made either way at this point.

I will say that I believe this particular boat will run on 2 gal/hour or less at wot, now if that is 15 mph instead of 20 mph the difference is not worth the time I took to type this sentence, now if the boat burned 10 gallons an hour and the difference in speed was 10 mph the difference would be huge like you mentioned.

If it wasn't so late I'd crush those numbers but my bottom feeder senses tell me that is a big difference.

I read somewhere that this hull shape tends to float over any waves bigger than 2 feet rather than crashing through them, which the writer attributed to a more "Physical" ride (like a bobber) but one he felt was inherently safer in bigger waves.

Again I am not a boat guy but I am curious what the characteristics of the boat are and what i might be able to do to make the most of this build situation.

If trim tabs are good, why wouldn't I just bolt the whole cavitaion plate system off the jet boat on? I still have it.

Neil

 

[laurentide]

That's true about floating over big waves. The boats don't have the weight or entry angle to cut through waves. That's also what makes the ride suck in bigger waves. So if you can slow down cruising speed and stay on plane the ride is better, but you'll still be working the throttle a lot.

That's the only drawback of the hulls IMO. They're safe, cheap to run, easy to fix, but can't be run at speed in 2-3 footers.

 

[g0nef1sshn]

I always liked moving comfortably in heavy seas rather than blasting through it (Atlantic not big lakes). If I was doing one of these bigger boats, I would run without the tabs first. You might build it with a good weight distribution load thats helps you plain out on its own. Then afterwards if you feel it would benefit to have, put them on like chemical stated.

 

[Watermann]

Yeah Ott I was just using those numbers as a for instance. Although if you were out of fuel and 5 miles from the dock, that would be HUGE. Not sure a guy could paddle one of those Chiefs very well. :lol:

My 18'r is actually 18' 11" and you said your Chief is 21' 5". There may not be much difference in the hulls but I would have to say that the AC plate from a jet boat that I don't think adjust to water conditions would not be the best as they don't project below the bottom of the hull.

So what's the HP rating on your diesel?

 

[Furrylittleotter]

I said I don't know much about boats. I know even less about diesels. From what I've read, it appears the horsepower varies on this motor based on (I think) which injection pump you have, or how the injection pump is setup. That being said, I think it is 40hp and 100 ft lbs torque. It is very hard to compare it to gas engines because it can ( and many do) run wot all day an all night.

I'm really trying g to learn more about water handling characteristics of th hull shape here but I'm not getting much.

When my neighbor (the marine surveyor) came over and looked at it in the air last night he remarked that it basically looked like a small "P.T." Boat. I looked at some photos and it actually does...

Now whether that will give me any clues about handling, remains to be seen.

Btw, if I mounted the cavitation plate on my boat, I would make it hinge. I doubt seriously I will. I mainly wNt to fish and if I lost a fish because a line got caught on that I'd be unhappy.

Neil

 

[laurentide]

One more minor thing about the smart tabs: when you're slow trolling, they're in the full down position. This helps the boat to track better and wander less. Not sure if you'll be trolling for certain species but it's a very minor yet noticeable difference.

 

[Furrylittleotter]

Ok I said I don't know much about boats and diesels, I know even less about trolling!

I have heard of some sort of "Trolling bag" (AKA sea anchor) which supposedly helps keep you straight as well, with the added benefit of keeping you pointed the right way should you lose power. I see the Amish make some...


Neil