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Author Topic:   Jet Drives

trevordiehl posted 11-20-2007 12:58 PM ET (US)
I am interested in opinions regarding the installation of a jet drive on a 1977 Sport. I live and fish on the Texas Gulf Coast which requires the ability not only to run in shallow water but the ability to get up in shallow water. I currently run a 40hp prop driven outboard which allows me to comfortably cruise at 35 mph but limits me to water a foot and a half or greater. I am concerned that a 35hp jet drive will reduce my top end speed as well as steering control. Any advice or experience with jet drives would be appreciated.
Mobjack posted 11-20-2007 01:42 PM ET (US)
Trevor, to achieve similar performance to your 40 prop, you will need at least a fity jet. Depending on who you talk to there is a 10-20% performance drop when you go to a jet. However, in a thirteen whaler you should be able to run as shallow as four to five inches with a jet drive.
As far as handling, I can't say what would happen. All my jet drive experience is in aluminum skiffs, with flat bottoms and tiller steering. In one of those, if you put the tiller hard over while at speed you could skid the boat around in a 180, and basically slide the back end around all over the place like a jet ski once you got the hang of it. That made for tremendous manueverability in tight spaces. However, on a tri-hull design like a whaler, I am not sure how those hard outer chines would respond to that kind of treatment...it might not work so well. Otherwise they are an absolute blast to drive.
After using them extensively in Alaska, I actually toyed with getting one for use at home in the shallows of the chesapeake bay, however I heard a lot of people talking about how they tend to not fare so well in a salt water environment where they could be prone to sucking up eelgrass and other vegetation. I think that use in areas with a lot of sandy bottom can also be bad, as the jet sucks a lot of sand into the impellor, which wears the sleave and the impeller itself much faster, and can also proceed upward into the lower unit.
I think the real indicator is that you don't see a whole lot of saltwater flats guides using them. In Ak they were widely used for running shallow rivers with gravel bottoms and clean water. I am sure it has been tried, and if they were able to work in an area like the keys, where running shallow is so important, I think they would have caught on down there, but you still dont see it.
Tohsgib posted 11-20-2007 02:00 PM ET (US)
I assume when you meant a 35 jet it was originally a 50hp and now is rated 35hp. I also agree with Mobjack on everything he said. You may want to try a jackplate for starters depending on what year your 40 is. My 1994 rude 40 on a jackplate with PTnT can run in less than a foot. If you really want to get creative, turn he hull into a tunnel and I bet 4" would be possible.
Mobjack posted 11-20-2007 02:26 PM ET (US)
Tosh, my four inch number is pure conjecture: I know that a forty horse jet on a 16 foot aluminum skiff running upriver can draw as little as 1-2", but I don't think you will see that type of performance out of a classic whaler hull, I think it will be more like four to six inches.
Scott W posted 11-20-2007 07:49 PM ET (US)
I run a 14 foot jet on numerous rivers in MI. It has a 25 HP head but is classified as a 20 HP motor. I used to run a 15 horse prop on the same boat and with two guys and gear in the boat the 15 prop and 20 jet are very comparible. With my flat bottom boat I can easily run in 2-3 inches of water. The only problem is you have to be running flat out and when you do hit something and you will in water like that it can leave a pretty good dent. I don't think I would even consider with a nice hull like yours. Also in the fall the leaves collect in the jet and cause me to shut it down and clean it out every 5-10 min when running. Leaves and weeds are a real pain but I would not trade that boat for anything in the river.
Dick posted 11-20-2007 11:14 PM ET (US)
I have owned and run numerous jet river boats both outboard and inboard, flat bottom and v bottom. The jet performs best on a boat with a slight v bottom. At speed the steering is just as good as with a prop but it does take getting used to at low speed. You will not have a true neutral as there is no gear box and there will always be water flow through the jet, again no problem once you get used to it.
You may get some info by contacting Boston Whaler, the commercial division used to configure the classic 15 hull for a jet outboard.
Mobjack posted 11-21-2007 10:20 AM ET (US)
you notice that all of us who have responded have run these boats in freshwater river situations. One thing he won't have to worry about is hitting anything, maybe an oyster bar now and then, but generally the gulf shallows have soft or sandy bottoms, and no big rocks like we had to contend with. I still don't think a whaler hull will slide as well as a metal skiff, and I think he might have trouble with sand and eelgrass being sucked in.
Dick posted 11-21-2007 12:39 PM ET (US)
My jet boat experience includes salt water use as well with no problems. I did clog an outboard jet once with sand when I had to slow to avoid another boat in a tight curve of the river, shut it off and it self flushed. Weeds and such are not much of a problem when at speed as the jet acts like a garbage grinder, it's at slow speed that clogging will happen.
Mobjack posted 11-21-2007 01:27 PM ET (US)
Dick the situation I worry about in salt and sandy bottom is a quick takeoff from shallow water...Where the boat is not on plane and the impellor grate is still right on the bottom..You punch the throttle, and until you get on plane that thing is digging and sucking...all that sand will chew up your impellor liner pretty quick..
Just running across a sandbar at speed would not worry me, its the takeoff.
While fishing in Florida this past year I watched our guide execute a shallow water takeoff with a propped 60 yamaha, our boat was a 17 foot flats boat, I can't remember the make, possibly a Hewes. Anyway, he performed the maneuver where you get up on plane by maintaining a sharp turn from the time you punch the throttle. It worked very well, and we were in shallow enough water where he never would have made it onto the step if he had run straight ahead and let the stern squat down.
Tohsgib posted 11-21-2007 03:01 PM ET (US)
That turn also works when you start bumping the bottom, just start zig-zagging and engine will be higher than going straight.
Dick posted 11-21-2007 11:05 PM ET (US)
It's been 25 years since I ran a jet boat and had forgotten about throwing the boat into a turn to get on step, now that you jogged my memory that was a normal practice.
Sand and silt won't have much effect on the impeller but will wear down the liner in the impeller housing. These can be replaced easily, we used to figure that if the clearance between the impeller and housing was over the thickness of a dime it was time to replace. The most damage to the impeller will be from gravel that is small enough to get through the intake grate, this can be cleaned up with a file and the impeller can made to last for years. The original outboard jet impellers were aluminum and quite soft and subject to damage, I believe that the impellers available now are either stainless or bronze.
Riptide23WA posted 11-22-2007 09:36 PM ET (US)
I posted this same question last January...
http://continuouswave.com/ubb/Forum4/HTML/005082.html
If you do it, I'd be very curious in the results...
Pat

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Author	Topic: Jet Drives
trevordiehl	posted 11-20-2007 12:58 PM ET (US) I am interested in opinions regarding the installation of a jet drive on a 1977 Sport. I live and fish on the Texas Gulf Coast which requires the ability not only to run in shallow water but the ability to get up in shallow water. I currently run a 40hp prop driven outboard which allows me to comfortably cruise at 35 mph but limits me to water a foot and a half or greater. I am concerned that a 35hp jet drive will reduce my top end speed as well as steering control. Any advice or experience with jet drives would be appreciated.
Mobjack	posted 11-20-2007 01:42 PM ET (US) Trevor, to achieve similar performance to your 40 prop, you will need at least a fity jet. Depending on who you talk to there is a 10-20% performance drop when you go to a jet. However, in a thirteen whaler you should be able to run as shallow as four to five inches with a jet drive. As far as handling, I can't say what would happen. All my jet drive experience is in aluminum skiffs, with flat bottoms and tiller steering. In one of those, if you put the tiller hard over while at speed you could skid the boat around in a 180, and basically slide the back end around all over the place like a jet ski once you got the hang of it. That made for tremendous manueverability in tight spaces. However, on a tri-hull design like a whaler, I am not sure how those hard outer chines would respond to that kind of treatment...it might not work so well. Otherwise they are an absolute blast to drive. After using them extensively in Alaska, I actually toyed with getting one for use at home in the shallows of the chesapeake bay, however I heard a lot of people talking about how they tend to not fare so well in a salt water environment where they could be prone to sucking up eelgrass and other vegetation. I think that use in areas with a lot of sandy bottom can also be bad, as the jet sucks a lot of sand into the impellor, which wears the sleave and the impeller itself much faster, and can also proceed upward into the lower unit. I think the real indicator is that you don't see a whole lot of saltwater flats guides using them. In Ak they were widely used for running shallow rivers with gravel bottoms and clean water. I am sure it has been tried, and if they were able to work in an area like the keys, where running shallow is so important, I think they would have caught on down there, but you still dont see it.
Tohsgib	posted 11-20-2007 02:00 PM ET (US) I assume when you meant a 35 jet it was originally a 50hp and now is rated 35hp. I also agree with Mobjack on everything he said. You may want to try a jackplate for starters depending on what year your 40 is. My 1994 rude 40 on a jackplate with PTnT can run in less than a foot. If you really want to get creative, turn he hull into a tunnel and I bet 4" would be possible.
Mobjack	posted 11-20-2007 02:26 PM ET (US) Tosh, my four inch number is pure conjecture: I know that a forty horse jet on a 16 foot aluminum skiff running upriver can draw as little as 1-2", but I don't think you will see that type of performance out of a classic whaler hull, I think it will be more like four to six inches.
Scott W	posted 11-20-2007 07:49 PM ET (US) I run a 14 foot jet on numerous rivers in MI. It has a 25 HP head but is classified as a 20 HP motor. I used to run a 15 horse prop on the same boat and with two guys and gear in the boat the 15 prop and 20 jet are very comparible. With my flat bottom boat I can easily run in 2-3 inches of water. The only problem is you have to be running flat out and when you do hit something and you will in water like that it can leave a pretty good dent. I don't think I would even consider with a nice hull like yours. Also in the fall the leaves collect in the jet and cause me to shut it down and clean it out every 5-10 min when running. Leaves and weeds are a real pain but I would not trade that boat for anything in the river.
Dick	posted 11-20-2007 11:14 PM ET (US) I have owned and run numerous jet river boats both outboard and inboard, flat bottom and v bottom. The jet performs best on a boat with a slight v bottom. At speed the steering is just as good as with a prop but it does take getting used to at low speed. You will not have a true neutral as there is no gear box and there will always be water flow through the jet, again no problem once you get used to it. You may get some info by contacting Boston Whaler, the commercial division used to configure the classic 15 hull for a jet outboard.
Mobjack	posted 11-21-2007 10:20 AM ET (US) you notice that all of us who have responded have run these boats in freshwater river situations. One thing he won't have to worry about is hitting anything, maybe an oyster bar now and then, but generally the gulf shallows have soft or sandy bottoms, and no big rocks like we had to contend with. I still don't think a whaler hull will slide as well as a metal skiff, and I think he might have trouble with sand and eelgrass being sucked in.
Dick	posted 11-21-2007 12:39 PM ET (US) My jet boat experience includes salt water use as well with no problems. I did clog an outboard jet once with sand when I had to slow to avoid another boat in a tight curve of the river, shut it off and it self flushed. Weeds and such are not much of a problem when at speed as the jet acts like a garbage grinder, it's at slow speed that clogging will happen.
Mobjack	posted 11-21-2007 01:27 PM ET (US) Dick the situation I worry about in salt and sandy bottom is a quick takeoff from shallow water...Where the boat is not on plane and the impellor grate is still right on the bottom..You punch the throttle, and until you get on plane that thing is digging and sucking...all that sand will chew up your impellor liner pretty quick.. Just running across a sandbar at speed would not worry me, its the takeoff. While fishing in Florida this past year I watched our guide execute a shallow water takeoff with a propped 60 yamaha, our boat was a 17 foot flats boat, I can't remember the make, possibly a Hewes. Anyway, he performed the maneuver where you get up on plane by maintaining a sharp turn from the time you punch the throttle. It worked very well, and we were in shallow enough water where he never would have made it onto the step if he had run straight ahead and let the stern squat down.
Tohsgib	posted 11-21-2007 03:01 PM ET (US) That turn also works when you start bumping the bottom, just start zig-zagging and engine will be higher than going straight.
Dick	posted 11-21-2007 11:05 PM ET (US) It's been 25 years since I ran a jet boat and had forgotten about throwing the boat into a turn to get on step, now that you jogged my memory that was a normal practice. Sand and silt won't have much effect on the impeller but will wear down the liner in the impeller housing. These can be replaced easily, we used to figure that if the clearance between the impeller and housing was over the thickness of a dime it was time to replace. The most damage to the impeller will be from gravel that is small enough to get through the intake grate, this can be cleaned up with a file and the impeller can made to last for years. The original outboard jet impellers were aluminum and quite soft and subject to damage, I believe that the impellers available now are either stainless or bronze.
Riptide23WA	posted 11-22-2007 09:36 PM ET (US) I posted this same question last January... http://continuouswave.com/ubb/Forum4/HTML/005082.html If you do it, I'd be very curious in the results... Pat