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Old 07-06-2019, 05:00 AM   #21
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Like everything a jet RIB has its pros and cons as a tender.

I bought a second-hand Avon Seasport 320 12 years ago or so and I still have it. It is 10' long, weighs 550 lbs. and packs an 80 hp 2-stroke Yamaha engine and jet drive.

At the time I wanted a dinghy that could also be used to take my children water-skiing but was small enough to be able to carry on the roof of the aft-cabin of my then boat a Grand Banks 42 Classic. Concerned about safety for the children, my wife valued a jet drive.

So I located and bought a second-hand jet (new ones are prohibitively expensive at $20k to $30k), installed a pipe davit and off we went.

I have used it for many years and have come to appreciate its advantages but admit it has some disadvantages compared to an outboard dinghy.

The main things I like about it are:

- wickedly fast acceleration and top speed of around 30 knots, which seems twice as fast in such a little thing so close to the water;

- no need to worry about hitting anything with the prop when coming ashore or having to raise the engine out of the water;

- safety when using with people in the water

- huge power and capacity in a very compact package: It would (just about) plane with me, my wife our three children and our two Labradors;

- easy to dock the mother ship while towing the RIB as there are no hard bits sticking out that can cause damage by hitting the boat or other boats.

- quite simple mechanically: there is no transmission with the turbine directly connected to the engine's output shaft and neutral and reverse achieved by orienting a scoop that will cover the jet nozzle; there is no water pump either, with high-pressure cooling-water simply drawn through the turbine casing.

The main disadvantages I found are:

- more expensive than similarly sized conventional dinghy

- quite heavy: when taking it to shore I would need anchor (with a clothes-line set-up) rather than simply pulling it up on to the sand;

- very hard to do work on the engine as it is hard to reach, at least in my jockey-seat model;

- very inefficient in terms of fuel consumption, probably in part because of the older 2-stroke engine but, I am guessing, the jet drive as well.

In terms of manoeuvrability I found it is actually superior. It behaves very different to an outboard-driven dink and so initially it appears to have terrible manoeuvrability. But after using several times one gets the hang of it and can dock it more elegantly than a conventional dinghy. It will, for example, turn around in place with no forward motion.

It is now almost 20 years old and I am not fully confident to take it longer cruises. My main dinghy now is a 13' Boston Whaler with a 40 HP outboard that I tow. That is also an awesome tender.
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Old 07-06-2019, 06:18 AM   #22
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Originally Posted by Xlantic View Post
Like everything a jet RIB has its pros and cons as a tender.

I bought a second-hand Avon Seasport 320 12 years ago or so and I still have it. It is 10' long, weighs 550 lbs. and packs an 80 hp 2-stroke Yamaha engine and jet drive.

At the time I wanted a dinghy that could also be used to take my children water-skiing but was small enough to be able to carry on the roof of the aft-cabin of my then boat a Grand Banks 42 Classic. Concerned about safety for the children, my wife valued a jet drive.

So I located and bought a second-hand jet (new ones are prohibitively expensive at $20k to $30k), installed a pipe davit and off we went.

I have used it for many years and have come to appreciate its advantages but admit it has some disadvantages compared to an outboard dinghy.

The main things I like about it are:

- wickedly fast acceleration and top speed of around 30 knots, which seems twice as fast in such a little thing so close to the water;

- no need to worry about hitting anything with the prop when coming ashore or having to raise the engine out of the water;

- safety when using with people in the water

- huge power and capacity in a very compact package: It would (just about) plane with me, my wife our three children and our two Labradors;

- easy to dock the mother ship while towing the RIB as there are no hard bits sticking out that can cause damage by hitting the boat or other boats.

- quite simple mechanically: there is no transmission with the turbine directly connected to the engine's output shaft and neutral and reverse achieved by orienting a scoop that will cover the jet nozzle; there is no water pump either, with high-pressure cooling-water simply drawn through the turbine casing.

The main disadvantages I found are:

- more expensive than similarly sized conventional dinghy

- quite heavy: when taking it to shore I would need anchor (with a clothes-line set-up) rather than simply pulling it up on to the sand;

- very hard to do work on the engine as it is hard to reach, at least in my jockey-seat model;

- very inefficient in terms of fuel consumption, probably in part because of the older 2-stroke engine but, I am guessing, the jet drive as well.

In terms of manoeuvrability I found it is actually superior. It behaves very different to an outboard-driven dink and so initially it appears to have terrible manoeuvrability. But after using several times one gets the hang of it and can dock it more elegantly than a conventional dinghy. It will, for example, turn around in place with no forward motion.

It is now almost 20 years old and I am not fully confident to take it longer cruises. My main dinghy now is a 13' Boston Whaler with a 40 HP outboard that I tow. That is also an awesome tender.

Interesting because we have had both and find these differences....

The main things I like about it are:

- wickedly fast acceleration and top speed of around 30 knots, which seems twice as fast in such a little thing so close to the water;
But outboards of similar HP on same sized RIBS will be faster...

- no need to worry about hitting anything with the prop when coming ashore or having to raise the engine out of the water;
Always had problems with debris sucking into the grate, it was possible to lift an outboard and/or see the potential offending items but not so with the hidden suction grate

- safety when using with people in the water
If the engine is not off nothing is safe.

- huge power and capacity in a very compact package: It would (just about) plane with me, my wife our three children and our two Labradors;
Again this is similar but less capable than a same sized outboard on a similar RIB.

- easy to dock the mother ship while towing the RIB as there are no hard bits sticking out that can cause damage by hitting the boat or other boats.
We had RIBS that were jet and RIBS that were outboards , no difference.

- quite simple mechanically: there is no transmission with the turbine directly connected to the engine's output shaft and neutral and reverse achieved by orienting a scoop that will cover the jet nozzle; there is no water pump either, with high-pressure cooling-water simply drawn through the turbine casing.
I have rebuilt the driveshaft, bearings and turbine wheel and housing in these jet drives. That along with engine work while the power plant resides in a closed space with little room needs to be experienced first hand. Any small particles that get drawn into these jets are always messing with the 0.008" - 0.012" clearances on the housing ,once the turbine tips and housing gets wear the time and money to attend is formidable.

The main disadvantages I found are:

- more expensive than similarly sized conventional dinghy
Agreed ...to buy, operate , repair and the depreciation.

- quite heavy: when taking it to shore I would need anchor (with a clothes-line set-up) rather than simply pulling it up on to the sand;
Mostly we kept it off of anything to avoid fouling and/or damaging the jet drives very small clearances.

- very hard to do work on the engine as it is hard to reach, at least in my jockey-seat model;
anything in there is hard to get to, anything.

- very inefficient in terms of fuel consumption, probably in part because of the older 2-stroke engine but, I am guessing, the jet drive as well.
Smaller boats of any kind that are offered in various drives like IO, outboard , and jet drives will have direct data comparisons between them. The jet drive is always less efficient in turning fuel into performance and as such will consume more fuel per mile and/or speed for the same HP.

The jet drives we had varied in the 80hp , 125hp and 200 hp range - but all had the same traits vs outboard counterparts.
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Old 07-06-2019, 06:21 AM   #23
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My understanding is that jet drives do not last long in salt water. Just my recollection.
Most all jet drives that we know about operate well and do not suffer from salt water use.
But if they are stored in salt water without a lift or dry dock most jet drives lack the salt water protection required for long term storage in salt water.
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Old 07-12-2019, 01:25 PM   #24
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A number of years ago I asked this question of a couple different jet drive tenders at the Miami Boat Show. I specifically wanted to know how they handled dissimilar metals in the drive units if the tender were left in the water behind the mother ship for days on end. They boat independently said the units were not designed to be left in salt water and should be lifted out when not in use. They both advised that a jet drive would not be appropriate for a tender to a recreational sized boat that didn't have the capability (or desire) of hauling the dinghy after use. That ruled them out for me.
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Old 07-12-2019, 01:36 PM   #25
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The jet casing and nozzle of my Avon Seasport are aluminum so it I try to limit the time it spends in the water. The RIB itself is not anti-fouled so that is another reason to avoid long spells in the water.

The jet does have sacrificial anodes so a month or two per summer has not been a problem.

Over the last 5 years I have towed the tender across the Mediterrraneanean several thousand miles to no ill effect.
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Old 07-12-2019, 02:10 PM   #26
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Probably 80% of the cost is for being cool.
Who needs that?

I’ll take an OB any day please.
I’s say “two stroke at that” but for a dinghy a small 4 stroke is better. Unless it’s one of these fast dinghys that aren't dinghies at all but runabouts. But people don’t use the word runabout now because they feel it’s not vogue enough.

For a real dinghy I’d want a 4hp twin cylinder OB. But it dosn’t exist. So I settle for my 4hp 2 stroke twin.
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Old 07-12-2019, 10:39 PM   #27
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The low speed handling is very poor, IMHO. As you approach the transom on your (real) boat, it is a complete lottery whether you will reach the desired location gently, or not at all, or in a manner/speed that will damage something. Over time, it turns into a real pain in the arse and you then go and buy a ‘conventional’ tender with an outboard.



H.
I had a Novarania 24 with a yanmar engine and a hamilton jet drive. Once you learn to handle them they are EXTREAMLY maneuverable at low speed. Trick is to keep the rpms up and use the bucket to control speed. I could come into a slip just a bit wider than my length, do a slow180 turn in place and head back out fully under control, just keep the throttle up, same with laying alongside. VERY MANEUVERABLE. Much more so than a tender with an outboard.

Pros were maneuverability, ability to go thru ice, no prop dings, would handle a good load, simple operation, can land on the beach.

Cons, heavy, sand tends to wear the drive when you do a lot of beach landings, slow acceleration if pulling skiers out of the water.

Otherwise. Great tender.

M
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Old 07-13-2019, 02:12 AM   #28
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We have jet tenders, love them, will not have anything else. We've had from 9' to 19'.

The pros:

-Shallow water usage. Don't go to 6" though. 2' is a good level.
-Speed. All we've owned have run at least 30 knots.
-Ride. We've compared the V's of our tenders and tested boats such as Boston Whalers on the same day in the same rough water and the jet ribs handled the roughness far better.
-Handling at speed. You can whip jets around while not rising up on your side. Short turn radius.
-Great for exploring where your main boat can't go easily.

The cons:

-Price. That's the single biggest reason you don't see more.
-Reputation of poor reliability based on some previous brands that used jet ski engines and set ups. We have Textron (was Weber) gas inboards and Yanmar diesels. Many used Yamaha jet ski engines and had the same maintenance issues as jet skis. Now, even the jet ski engines have improved. Williams has now gone to Rotax. I haven't used one yet. Also, we've owned Avon Seasport Jet Tenders which basically are interchangeable with Williams so same pluses and minuses but they are not sold in the US. Novurania has great jet tenders but all larger and much heavier.
-Weight is a disadvantage of the diesel jets. Weight on the gas units isn't bad.
-Handle differently than you're use to, especially at low speed. I won't say they handle poorly at low speed because I don't think they handle any poorer than single outboard ribs once you learn to operate them. You use their power and can do so effectively. It's just different than what you've ever done before. You may ease an outboard into reverse, but you don't ram it hard into reverse. You can do that with jets without damage.

I'll be glad to answer any specific questions.
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Old 07-13-2019, 02:17 AM   #29
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Adding a couple of comments. No outdrives, jet or outboard, are best left in salt water and not flushed.

Captmikem mentions sand damage. That does occur with those who try to run in under one 1 of water in sand. If you're going to beach you need to turn it off in advance of extreme shallow water, much as you would an outboard. You'll also pick up growth and other things in some areas in extremely shallow water and have to remove it. We try to run in 2' or more and have never had an issue.
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Old 07-13-2019, 06:05 AM   #30
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I had a Novarania 24 with a yanmar engine and a hamilton jet drive. Once you learn to handle them they are EXTREAMLY maneuverable at low speed. Trick is to keep the rpms up and use the bucket to control speed. I could come into a slip just a bit wider than my length, do a slow180 turn in place and head back out fully under control, just keep the throttle up, same with laying alongside. VERY MANEUVERABLE. Much more so than a tender with an outboard.

Pros were maneuverability, ability to go thru ice, no prop dings, would handle a good load, simple operation, can land on the beach.

Cons, heavy, sand tends to wear the drive when you do a lot of beach landings, slow acceleration if pulling skiers out of the water.

Otherwise. Great tender.

M
Interesting - we had a 19' Nautica with a 115 Hp outboard and also a 19" Nautica with a 200 Hp jet drive. The advantage was justt about always with the outboard. The jet had problems with fouling the intake grate and get casing in the Hudson as well as many places in Long Island sound with various types of sea weed. Turbid water when exploring in areas of the Hudson, Ct river, Mystic, BI, Montauk etc were rough on the jest drive impeller and case edges. The lower hp outboard was lighter , faster, and handled well in rougher water except for the fact that it could not spin on a dime. Service was easier and efficiency was better even with the jet being a diesel.
FWIW - the 19' Nautica with 115 outboard could reach 52-52 mph, about 10 mph faster than the 19' Jet with higher hp.
We also had a 24" Nautica with outboards that could reach near 70 mph.
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Old 07-13-2019, 11:00 AM   #31
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Bombardier Sportster Jet boat tender

We love our Sea Doo jet boat’s dry, smooth ride, serviceable at any Sea Doo place. We tow it outta the way with our Towdster bars.
Of course the captain had to supercharge it, it will reach 70 mph, what’s that in knots?
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Old 07-13-2019, 01:22 PM   #32
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We love our Sea Doo jet boat’s dry, smooth ride, serviceable at any Sea Doo place. We tow it outta the way with our Towdster bars.
Of course the captain had to supercharge it, it will reach 70 mph, what’s that in knots?
The size and sophistication of a tender is usually a function of the size of the mother vessel. For instance, larger vessels can find tenders with twin inboard engines with a capacity of dozens of people practical.
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Old 07-13-2019, 01:30 PM   #33
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We love our Sea Doo jet boat’s dry, smooth ride, serviceable at any Sea Doo place. We tow it outta the way with our Towdster bars.
Of course the captain had to supercharge it, it will reach 70 mph, what’s that in knots?

Our friends had a twin engine sea doo speedster, it was a nice boat....
https://www.topspeed.com/boats/sea-d...r-ar36172.html
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Old 07-13-2019, 01:40 PM   #34
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Ok
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Old 07-13-2019, 02:09 PM   #35
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BM,
Like your toadster bars.
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Old 07-13-2019, 02:15 PM   #36
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Towdster In-Water Towing Device
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Old 07-13-2019, 05:05 PM   #37
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Interesting - we had a 19' Nautica with a 115 Hp outboard and also a 19" Nautica with a 200 Hp jet drive. The advantage was justt about always with the outboard.
What engine and drive on the Nautica? Nautica died before our first RIB purchase so never learned that much about them.
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Old 07-13-2019, 05:11 PM   #38
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This RIB with outboards was easy to tow and only needed about 10" pf water or so....

https://pix.sfly.com/DTrBaR

https://pix.sfly.com/3ehvse
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