Boat Testing

[NightTrain]

Took the boats out on Big Lake today for a couple hours to test out my son's new boat & make sure she's healthy. Both ran like champions.

Beautiful day!

http://www.debatepolicy.com/attachment.php?attachmentid=8902&stc=1
http://www.debatepolicy.com/attachment.php?attachmentid=8903&stc=1
http://www.debatepolicy.com/attachment.php?attachmentid=8904&stc=1
http://www.debatepolicy.com/attachment.php?attachmentid=8905&stc=1
http://www.debatepolicy.com/attachment.php?attachmentid=8906&stc=1

[NightTrain]

http://www.debatepolicy.com/attachment.php?attachmentid=8907&stc=1

[Gunny]

Your son just needs to give the boat to you. You're prouder of it than he is.:laugh:

[NightTrain]

Your son just needs to give the boat to you. You're prouder of it than he is.:laugh:

Yeah, I am pretty proud of him.

[Gunny]

Yeah, I am pretty proud of him.

Understand. Totally proud of my daughter too. Thought I was going to have to kill her when she was a teen. She turned out to be better than me. And I don't mean that monetarily. So I get it. I just wish she would get a damned boat. :laugh:

[Elessar]

Nice NT! This is something a Coastie Bos'un can do!

[Gunny]

Nice NT! This is something a Coastie Bos'un can do!

I'm curious about the boat itself. I'm not used to something that small. I'm completely ignorant to fresh water and boats. It looks cool. I just know what it's like to be a proud father and brag on your kid. Kudos to NT.

[CSM]

Frikkin awesome!!!

[NightTrain]

I'm curious about the boat itself.


These boats are specifically designed to run in very shallow water - about 3". Any less than that and the hull will hit bottom, and at that point you're sucking gravel & sand through your jet unit which is very hard on it. Do that a few times and you'll be replacing the impellers inside the jet unit which is expensive and a pain in the butt. Essentially, the jet units are just big water pumps - instead of a propeller in the water, the jet sucks in water from the bottom of the boat and spits it out the back of the boat at high velocity.

To enhance the shallow water capability, the impellers inside the jet are more of a "hole-shot" variety... designed to get your boat from a standstill to up on step (hydroplaning) in about one or two boat lengths, depending on how heavy you are - the more load you have, the longer it takes to get up on step. Of course, there's always a trade off on something like this, and what you lose in a riverboat is top end speed. You'd think that these boats would hit 70 MPH, but top speed on my boat and my son's boat is 44 MPH, and that's with the engines howling at red line. Cruise speed is about 33 - 35 mph.

They're made from 3/16" marine grade aluminum, and you know what that stuff is like - extremely tough and lightweight. That means you can bounce off rocks, jump logs, hit gravel bars and the like with usually only a cosmetic scratch left from the incident. I've punched holes in the hull from hitting a sharp boulder when running whitewater, but usually it's a small hole that the bilge pump can keep up with until you get back to the trucks, and a local boat shop can pound out the dent and weld up the offending leak in the hull for a hundred bucks or two.

The hull design for shallow water running is more of a flat bottom than you'd see in an ocean boat or lake boat - the boats we have are "semi-V" hulls, rather than a V. Some are outright flat bottoms. The trade off is that instead of cutting through waves like a V hull, these will stay on top of the waves which results in beating you half to death. In whitewater, because you're on top of standing waves, the jet will sometimes cavitate, which means it sucks air instead of the water, resulting in a momentary (hopefully) loss of thrust and steering and the engine RPM spikes because there's suddenly no load on it. This would be comparable to running down the road in your stick shift truck at 3/4 throttle and pushing in the clutch for one second and dumping the clutch - the engine screams and then resumes the load after a second... kind of hard on things but the engine and jet are built to handle that kind of abuse. Still, I don't like to hear my engine do that! :laugh2:

Since there's nothing in the water to steer like you'd have with a prop, your steering is 100% dependent on thrust from the jet. There's a nozzle at the back end of the jet that directs the water left and right (and some even adjust up and down for trim), so if you don't have any throttle on, you have no steering. I've seen a couple of knuckleheads come in hot to a crowded boat launch, chop power, and then turn their wheel - the boat keeps going straight ahead and plows into very expensive boats sitting there at the launch. At that point there's a very animated discussion about the hapless driver's family tree and who's going to pay for the new hole in the side of a painted hull.

Anyway... that's a basic breakdown of these particular boats.

[Elessar]

There are lots of jet-drives on the rivers out here and many have a small prop-job kicker for
close-in maneuvering.

One of the newer CG small boats is a jet drive, 45 foot response boat (RB-M). I just wonder about towing
another boat with it.

http://www.uscg.mil/acquisition/rbm/

[NightTrain]

There are lots of jet-drives on the rivers out here and many have a small prop-job kicker for
close-in maneuvering.

Yeah, I have a 20 hp outboard prop kicker that I haven't mounted on my boat yet... it's good to have a Plan B for when something happens to the main and you're floating down towards a nasty set of sweepers! There's no way you can paddle these boats in the fast moving rivers we play in. I need to do that soon.


One of the newer CG small boats is a jet drive, 45 foot response boat (RB-M). I just wonder about towing
another boat with it.

http://www.uscg.mil/acquisition/rbm/


I've towed quite a few boats over the years that lost power on the river & lakes with no problem. I'm guessing you're wondering about the effect of the rooster tail from the jet hitting the other vessel? That doesn't become a factor until you're getting up on step and then it erupts over the surface, but all the towing I've done was at slow speeds.

If you did want to tow at hydroplaning speeds, you'd just give enough line for the other boat to be far enough behind so the rooster wasn't washing against the towed vessel's hull.

I've been reading about big Navy ships using jets instead of props in the last few years... I wonder if that's the future of water propulsion.

[CSM]

I would think that a loss of steerage when power cuts off would be a concern in some situations. That and no reverse.... For me, I'll take the twin screws and rudders for better maneuvering at lower speeds, though I do understand the shallow draft, high speed requirements for the type of boating going on here.

[Gunny]

These boats are specifically designed to run in very shallow water - about 3". Any less than that and the hull will hit bottom, and at that point you're sucking gravel & sand through your jet unit which is very hard on it. Do that a few times and you'll be replacing the impellers inside the jet unit which is expensive and a pain in the butt. Essentially, the jet units are just big water pumps - instead of a propeller in the water, the jet sucks in water from the bottom of the boat and spits it out the back of the boat at high velocity.

To enhance the shallow water capability, the impellers inside the jet are more of a "hole-shot" variety... designed to get your boat from a standstill to up on step (hydroplaning) in about one or two boat lengths, depending on how heavy you are - the more load you have, the longer it takes to get up on step. Of course, there's always a trade off on something like this, and what you lose in a riverboat is top end speed. You'd think that these boats would hit 70 MPH, but top speed on my boat and my son's boat is 44 MPH, and that's with the engines howling at red line. Cruise speed is about 33 - 35 mph.

They're made from 3/16" marine grade aluminum, and you know what that stuff is like - extremely tough and lightweight. That means you can bounce off rocks, jump logs, hit gravel bars and the like with usually only a cosmetic scratch left from the incident. I've punched holes in the hull from hitting a sharp boulder when running whitewater, but usually it's a small hole that the bilge pump can keep up with until you get back to the trucks, and a local boat shop can pound out the dent and weld up the offending leak in the hull for a hundred bucks or two.

The hull design for shallow water running is more of a flat bottom than you'd see in an ocean boat or lake boat - the boats we have are "semi-V" hulls, rather than a V. Some are outright flat bottoms. The trade off is that instead of cutting through waves like a V hull, these will stay on top of the waves which results in beating you half to death. In whitewater, because you're on top of standing waves, the jet will sometimes cavitate, which means it sucks air instead of the water, resulting in a momentary (hopefully) loss of thrust and steering and the engine RPM spikes because there's suddenly no load on it. This would be comparable to running down the road in your stick shift truck at 3/4 throttle and pushing in the clutch for one second and dumping the clutch - the engine screams and then resumes the load after a second... kind of hard on things but the engine and jet are built to handle that kind of abuse. Still, I don't like to hear my engine do that! :laugh2:

Since there's nothing in the water to steer like you'd have with a prop, your steering is 100% dependent on thrust from the jet. There's a nozzle at the back end of the jet that directs the water left and right (and some even adjust up and down for trim), so if you don't have any throttle on, you have no steering. I've seen a couple of knuckleheads come in hot to a crowded boat launch, chop power, and then turn their wheel - the boat keeps going straight ahead and plows into very expensive boats sitting there at the launch. At that point there's a very animated discussion about the hapless driver's family tree and who's going to pay for the new hole in the side of a painted hull.

Anyway... that's a basic breakdown of these particular boats.

I got news for ya, bubba. If you think there's a squid or jarhead on this board that doesn't know what a flat bottom does in the ocean .... :laugh2: Try an old LPA. You spend a LOT of time trying to avoid the guys puking their guts out. Those things spend their time trying to see just how bow under they can go. Love to corkscrew. Nothing like rocking and rolling. :laugh:

The boat you're talking about is intriguing to me. I've never driven one with a jet. Actually, I've never seen one with a jet that I know of. Looks like loads of fun.

[NightTrain]

I would think that a loss of steerage when power cuts off would be a concern in some situations. That and no reverse.... For me, I'll take the twin screws and rudders for better maneuvering at lower speeds, though I do understand the shallow draft, high speed requirements for the type of boating going on here.

It does take getting used to, but my boat at idle will spin on it's axis within it's own length with the wheel cranked.

And there is reverse! There's a bucket that drops down over the end of the nozzle and diverts the flow of water back under the boat. In an emergency you can throw her into reverse and goose it, and you'll quickly stop... about the closest thing to brakes that you can get for a boat.

In this pic, the bucket is raised out of the way, so you'd be in Forward mode :

http://www.debatepolicy.com/attachment.php?attachmentid=8910&stc=1

In neutral, the bucket drops down and splits the flow of water in half; so half of the flow gets diverted back under the boat and half continues out normally, resulting in no forward or backward movement but still providing steering. Pretty ingenious.

The problem with the bucket is that it's the first thing that breaks - you've got an extra cable & linkage all hanging out there on the back of the jet, so any kind of impact from another boat or drifting into something will foul up that whole system in short order. We've got protective aluminum bars around it, but any damage always seems to zero in on that area... Murphy's Law and all that.

[Elessar]

Yeah, I have a 20 hp outboard prop kicker that I haven't mounted on my boat yet... it's good to have a Plan B for when something happens to the main and you're floating down towards a nasty set of sweepers! There's no way you can paddle these boats in the fast moving rivers we play in. I need to do that soon.

I've towed quite a few boats over the years that lost power on the river & lakes with no problem. I'm guessing you're wondering about the effect of the rooster tail from the jet hitting the other vessel? That doesn't become a factor until you're getting up on step and then it erupts over the surface, but all the towing I've done was at slow speeds.

If you did want to tow at hydroplaning speeds, you'd just give enough line for the other boat to be far enough behind so the rooster wasn't washing against the towed vessel's hull.

I've been reading about big Navy ships using jets instead of props in the last few years... I wonder if that's the future of water propulsion.

Well....I've towed literally hundreds and you have to determine the hull speed of the one being towed, allow enough tow line out
for catenary, and keep a watch on the tow. If you grab that tow line and it feels warm or vibrating, let more line out. I'd never use
polypropylene as a tow line! It is too brittle. Three-strand or double braid nylon are better, with the DB being the best.

Best place to tow one from is the trailering eyebolt, provided it has a secure backing plate.