Just a question regarding Jets vs protected props

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richg99
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Just a question regarding Jets vs protected props

Post by richg99 »

Now, I know NOTHING about Jets.

On a cruise last week, I took a couple of pictures of protected props on the life boats. Since Jets lose so much power....i.e 60 hp is effectively 40 hp???....I wondered if using similar protection devices on a propped boat wouldn't give 90% or so of the rock protection, with an increase in effective horsepower and speed.

Remember, I said I know NOTHING about jets. What say you all? richg99

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RivrLivn
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Just a question regarding Jets vs protected props

Post by RivrLivn »

Well the reason those boats have those is because the Coast Guard requires lifeboats to have propeller guards.

The point of a jet is to have nothing or almost nothing(outboard jets) sticking below the bottom of the hull.

Even with the propeller guard on those boats if you would hit a log or rock ledge at speed, that would be a baaad thing. :oops:

openseat
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Just a question regarding Jets vs protected props

Post by openseat »

The examples above are more to protect people than props. There are somewhat similar devices for prop protection that are used on (generally) smaller outboards with unlocked manual tilt. The guard bounces/eases the outboard over obstructions. Google “rockhopper”, for one of the more common versions of that type.

The downside is that you can’t hop the motor like that at planing speed. If you’re only occasionally going through jet-type areas, and if you are willing to go slow, it can be a good accessory for a small prop motor.

My neighbor has an inboard jet, but he also keeps a kicker motor with a prop guard on board as plan B when he is running rivers downstream from his launch site.

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SaltyGhost
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Just a question regarding Jets vs protected props

Post by SaltyGhost »

The previous posters are correct. Jet boats are for going into the shallows and running over water hazards without damaging your motor/lower unit.

The covered prop thing is actually in use already. The U.S. military actually buys outboards from Evinrude with a encased prop for use on Zodiac type boats.
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dhoganjr
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Just a question regarding Jets vs protected props

Post by dhoganjr »

As mentioned above, the rockhopper protected outboards are made to occasionally get into the shallows and protect the prop from damage by kicking the motor up at slow speeds when you hit something. Anything at moderate speed or above is still more than likely to cause damage to the lower unit. Properly built tunnel hulls can run shallow down to maybe 10-12", but you still run the risk of damage if you hit bottom.

A jet is built for shallow running at planing speeds down to 2-3" of water. You still need deeper water for starting out and stopping in but once on plane about an inch of the shoe is below the boats hull. A jet is more forgiving if you do hit. A tree or stump usually you just slide over it. In gravel bottom streams if you hit most of the time it will suck rocks up in the grate and you have to stop and clean them out. The shoe is made of cast aluminum so if you hit a good sized rock or boulder just under the surface at speed you run the risk of busting a chunk out of it. This can be fixed by an experienced welder or by buying a new one at about $400. So, while they are built for running shallow, they are still at risk for being damaged when you run the extreme shallow areas. I have ran jets for about 14 years and have busted 1, so while it can happen, it is a rare occurrence.

I spend about 90% of my boating time on the river, mostly clear gravel bottom streams here in the Ozarks and that is where jets shine. I still feel sorry for the prop guys cussing and churning mud in the channel as I swing wide and wave going by a few feet off the bank.

You can overcome the hp loss with a bigger outboard or by building up the engine, depending on what it is.
Dan
2003 1860 Alweld Flat Bottom
2014 Mercury 250 Pro XS Jet
2003 RiverCraft trailer
Retired from Riverlife-2002 Mercury 115 Fourstroke Jet

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