15ft StarCraft V8 and jet conversion

Discussion in 'Jet Drives' started by sm465np205, May 17, 2019.

  1. sm465np205
    Joined: May 2019
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    Location: Michigan

    sm465np205 Junior Member

    New here figured I'd share my current project. Started with a 15 ft aluminum hull with a small outboard. Marinized a '05 4.8l gm LS V8 engine. Mounted a Berkeley 12jc pump with a trim nozzle in the boat. Have done a lot of welding in reinforcements and I'm almost ready to weld in the stringers and install the engine
     
  2. sm465np205
    Joined: May 2019
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    Location: Michigan

    sm465np205 Junior Member

    IMG_20190417_210450085.jpg IMG_20190415_190054062.jpg
     

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  3. sm465np205
    Joined: May 2019
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    sm465np205 Junior Member

    Any insight or pointers would be greatly appreciated! Building this to run local rivers that are littered with logs so I will be covering the entire bottom with uhmw
     
  4. Mr Efficiency
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    Mr Efficiency Senior Member

    What do you expect the finished weight will be ? Might be a lot for a smallish boat.
     
  5. Yellowjacket
    Joined: May 2009
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    Yellowjacket Senior Member

    Your biggest issue is that the CG is way forward from where it originally was on that hull. This could lead to serious instability at the speeds that you can easily get to with this rig. That is, you could easily find yourself looking from whence you came in about a half a heartbeat. We recently had that issue with a small unmanned hull and above a certain speed it would grab and bow steer with the slightest excuse, like crossing a small wake. With the outboard the CG was much further aft which kept the nose up, and there was a nice deep skeg and lower unit in the water and this kept the hull pointy end going forward. Without that stuff in the water you have a potentially serious instability problem. Having some v in the hull helps, but you can easily get that running fast enough to be mostly on the bottom of the V. I would look at the Aussie jet sprint boats and see what they use to keep the boat pointing in the proper direction. Some of them use two one inch deep two inch long skegs on the aft bottom. Those boats are typically doing around 50 knots because of the tight course, but out in the open water they'd be a lot faster. They trim nose down because they want the boat to turn on a dime. You don't want the boat to do that because it's really inefficient and as I said, at higher speeds it becomes unstable. The trimmable nozzle is essential, but that may or may not be enough to keep you from getting into trouble.
     
  6. Mr Efficiency
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    Mr Efficiency Senior Member

    Anything with a pronounced forefoot is a real concern, for a high-powered jet boat with little deadrise aft. And especially if it will need to run at a lively speed to keep it up and running cleanly, which seems likely with the weight of a V8 in a small boat. Proceed with caution, hull selection is critical with jet boats.
     
  7. sm465np205
    Joined: May 2019
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    Location: Michigan

    sm465np205 Junior Member

    Good question hard to say for sure on the weight. The pump is roughly 140 lbs altogether with the intake. The engine is an iron block over 400 lbs. 19 gallons of fuel in the bow and we're moving the dash, windshield and seating forward 8". Not sure what the hull weighed but it was just about nothing. If need be, the aluminum block variants are over 100 lb less, but I'm gonna try it with the more plentiful truck engine first. Spoken with quite a few gentlemen in Canada and new Zealand running 14 and 15 ft boats with identical, similar or in most cases heavier powertrains (all iron small block Chevrolet or Ford, Hamilton 212). Most recently spoke with someone in Alberta using an iron block 6.0 and an American turbine pump, which is literally within a few pounds of this setup. He was kind enough to describe his hull dimensions to me, which has the same deadrise, same beam and is a foot shorter at 14ft. Now I understand there are a thousand other variables, and also that shooting from the hip strictly based on other boats basic weight and hull dimensions is no way to build a boat. However and I don't want to come across as reckless but this is going to be an exercise in utilizing what is plentiful to possibly create something that works to a certain degree but quite obviously isn't 100 % ideal. These folks I've spoken with are running in mere inches of water, but very clear water in which obstacles are somewhat visible. The local rivers to me are relatively deep at least within their distinct channels, but are very murky. There are few rocks or gravel, but there's a large amount of saw cut logs. Most of these logs largely remain stationary and can be avoided, but some obviously move around with the frequent flooding cycles we have. The only thing I'm trying to accomplish is travel at the slowest speed possible while still on plane and be able to withstand the occasional contact with a log, something my 18ft glass jet could only take so much of before I had to retire it from river duty. If the boat draws even 8 to 10 inches at this comfortable and safe speed, that'll still be fine. The slower the better, as I don't want to run over a canoe or Jon boat because I was being careless. I firmly believe the trim function of this pump is the key to accomplishing this, as the same nozzle installed on my other boat did absolute wonders for it. Not only does it allow the boat to plane instantly with practically no bow rise, but I can travel at a much lower speed on plane. If you're familiar with the place diverter you know the amount of trim its capable of is almost extreme and unnecessary up and down. I may be wrong but I think it will at least somewhat make up for some of the apparent deficiencies of this hull. My friends don't believe me but I don't plan on pushing this boat at high speeds; it's too dangerous as the hull is not even remotely designed for it. I originally was going to use a 295 HP 5.3l I have, but decided to step down to the 270 HP 4.8l. Mainly just to lower the power and maybe help resist the temptation to do stupid things with the boat, as the 4.8, 5.3 and 6.0 all are basically the same weight. But I also figured it would give me marginally better fuel economy. I'm rambling at this point. I really appreciate the comments let me know what you think. If I'm being an idiot please tell me haha. I'll keep you guys updated with the progress
     
  8. Mr Efficiency
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    Mr Efficiency Senior Member

    It is the forefoot area that is the problem, the less the better for avoiding directional instability.
     
  9. Barry
    Joined: Mar 2002
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    Barry Senior Member

    Some random comments

    You mention that you have had feed back from some Albertans who said that they have the same size of boats, true length breadth, maybe, but I never have seen a large inboard engine installed in a thin shelled riveted aluminum hull. The reason they rivet is that welding is more expensive, welding will induce distortion in thin skins, and most riveted hulls
    are not intended to bounce around off rocks or logs in a river.

    While you can certainly add stringers to stiffen thin material, it is better to start with a thicker hull bottom. We used 3/16 inch once and had a lot of issues with distortion and flex, then went to 1/4 inch bottoms and 1/8 inch sides.

    With the 3/16 we had to add a lot more weight for stiffeners so we found that the weight difference between 3/16 and multiple stiffeners and 1/4 inch with less stiffeners, was insignificant


    What impellor are you intending to run?

    There are a few very important areas that are weak.

    The area in front of the intake. Say you hit a rock at 30mph on the keel line, the hull will flex at this point and the flex indentation,( not permanently, but could be) will run from the point of
    impact down toward the stiff intake casting. Two things can happen, the intake will break or the weld immediately ahead of the intake will crack.
    This flex will misalign the pump to motor concentricity and import a huge stress on the casting that the pump bowl sits in. The result can be a catastrophic failure of this casting with an immediate sinking. The boat that we built with the 3/16 bottom exhibited this event.

    While we cannot see the inside of the transom, I cannot see any weld print through to suggests inside strengthening members. Regarding the flex in the transom causing
    the bowl casting to break has to be reduced. A 1 1/2 x 3 1/2 inch by 3/16 inch angle running transversely just above the pump to the sides of the boat and also vertically
    down on either side of the pump will help, though with the thin bottom material this might be difficult.

    The corner welds need to be addresses. Again, thin material = excessive flex = a propensity for weld cracks at the upper transom to side joint.
    A triangular gusset say 8 x 8 or larger, welded at the to of the gunnel to the transom, with NO welds crossing the gunnel or transom at 90 degrees, stitched, say 2 inches skip 2 then 2 inch
    would help. You should radius, concave, the hypotenuse.

    We have repaired quite a few boats for weld failure in this area.

    I suspect you are going to deal with the keel strip sharp transition into the intake?

    On our river boats we used 1/4 inch bottom material, welded in a Best Casting, not sure if they are around any more but used them for Berkleys, preheat the casting before welding,
    after cooling, we would weld in a 6 inch by 1/2 inch flat bar down both sides of the intake to the transom and forward 5 feet up. In front of the intake, we would take 6 x 1/2 flat bar and on
    the inside weld two pieces on the keel line, laid flat forward until the keel began to curve upward. On the inside so as not to restrict flow into the intake.

    Then one more layer of 1/2 inch flat bar from the transom about 1 foot ahead of the intake. We used this thicker material to attach the vertical members noted above that went along side the
    pump.
    Note that most serious river boat manufactures do not use the transom casting but split the bowl and bolt the housing through the transom.

    With the jet-0-vator and the JC configuration, your pump is seriously exposed. If you do hit a log, the hull will hopefully ride over it, lifting the boat until the transom clears
    then the pump drops down on the extended pump. Usually what will break is the casting where the steering pins are located.

    It appears that you are using the Berkley grate. Berkley and American Turbine, mixed flow pumps have a tremendous dislike for small rocks caught in the fingers of the intake or even
    small rocks, sticks that make their way into the bowl. Most river jet boats utilize a clean out grate where every second finger can be moved down from the top, to clear these rocks.
    In the event that this type of grate will not clean the bowl, then you have to access the bowl through the pump inspection plate. With the smaller size of your boat and the heavy powerplant
    you should purchase an inspection plate extension so you can take the inspection plate off without an ingress of water into the boat. You need quite a bit of relief above the inspection
    opening at the transom

    While we started out using Berlkey, with all the issues of debris, we switched to the Kodiak 3 stage, awesome pump, a little noisey, then graduated to the Hamilton 773, noisey as well.
    then moved up to the Hamilton 212. The 212 was the best of the pumps. Normally anything that would go through the intake fingers went out the back end.


    But it appears that maybe you will not see hard running though you mention logs and rocks so maybe you will be lucky and not have any problems
     
  10. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    I would say the structure of the boat was not designed for the power and speed you are adding. Most likely the hull will fail.
     
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  11. sm465np205
    Joined: May 2019
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    sm465np205 Junior Member

    Thank you Barry lots of good points here.

    The reference I made about the similarities between this hull and the hulls used by these folks I spoke with was strictly in regard to buoyancy, and the boats potential ability to sustain the extra weight. I understand that a purpose built river boat hull is made using substantially thicker materials. My hope is that reinforcements in strategic areas of the hull will yield something sustainable.

    I'm glad you mentioned the front of the intake as a potential catastrophic failure point, as I've experienced this first hand with my other boat. As we traversed a log along the keel, there was enough give in the fiberglass to cause the log to abruptly contact the front edge of the intake casting, breaking the intake and actually splitting the entire suction housing above it in half. Fortunately the crack didn't open up enough that the bilge pumps couldn't easily keep up, and I was able to limp it the rest of the way up the river to the ramp. Lots of damage that I've since repaired. So I agree this particular area needs to be extremely strong. It's already over a 1/4" thick with the material I've welded on the inside. On the bottom, the front edge of the intake actually protrudes below the keel 3/8", as the boat it was salvaged from had a slightly deeper vee. So I can weld a 3/8" thick plate directly in front of the intake and still have a smooth transition, while also strengthening the area. The custom flange I made for the intake to rest in is 3/8x2 bar on top of 1/4x4 bar. The 2x6x1/4 stringers will be just outboard of the flange, and I planned on gusseting from the top of the stringer down at an angle to meet the intake flange just outside the casting. This would mean in order for the intake to shift upward from an impact it would also have to take the stringers up with it. Hopefully these measures combined with the new much stronger transom will keep the intake intact and in place?

    The pump currently has an A impeller, which is obviously poorly suited to a 270HP engine. I've spoken with quite few experts in this regard and the consensus seems to be try a B, C or B/C cut. In order for the small engine to reach peak power at almost 6k rpms, it would require a D cut, which I'm told would be so inefficient at low speeds the boat would have trouble planing. I planned on running the A initially and acquiring a few other As to send out and have different cuts done on each so I can experiment.

    I'll certainly heed your advice on the corners where the transom and gunwale meet; I knew it would need some attention but haven't addressed it yet. And yes the keel strip has been cut forward a few feet and the tapered end that was cut off the stern end has been welded back on. I was going to completely remove the strip and replace it with a wide thick flat bar along the entire keel? I still may do so but in the interest of getting the boat in the water as quickly as possible, this may be another thing I do after I'm sure the boat will actually function.

    In regard to the excessive pump stick out, I planned on tubing running longitudinally on either side and below the pump, then radiused up at the nozzle to meet a swim deck of sorts. This seems to be the common solution to protect against landing on the pump in most applications? And yes the Berkeley approach to a grate is certainly half hearted; leaves a lot to be desired. I think the best route here is fabricating an entirely new grate. One that uses perhaps thinner fingers, but more of them. I've removed enough rocks from in between the bowl and the impeller of the other boat to realize these grates are inadequate for what I'm trying to do

    Mr efficiency I'm assuming you are referring to the fact that these hulls have more of an axe bow configuration as opposed to a more gradual radius like what is used on a typical river going boat?

    Gonzo you are 100% correct it most certainly isn't made for anywhere near a 400 lb engine with 270 HP lol. Hopefully the countless hours of welding will make it stay together we shall see
     
    Last edited: May 20, 2019
  12. gonzo
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    gonzo Senior Member

    I think that you should continue the stringers forward until they meet the chines. That may help keep her together.
     
  13. Mr Efficiency
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    Mr Efficiency Senior Member

    Yes, and combined with shallow vee aft. The StarCraft glass boat in that size range seems a much more apt shape for jet.
     
  14. Barry
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    Barry Senior Member

    I would suggest starting with the A2 ( even an A3 cut) impellor . If it is too steep, then you can cut this back. Can you post the HP curve for your engine?
    I would not consider trying to match an impellor for 6ooo rpm. If you get the proper match and can only turn out say 4200 rpm at max, the engine will give you better longevity and
    better fuel consumption.

    We used the A3 impellor on 320 hp engines. Could only max out around 4200 prox. But we kept ( I wish I could find the tables) fuel consumption vs rpm vs speed, (floscan metering)
    and found that the A3 in this configuration provided the best fuel economy at 30 mph for a 3500 - 4000 pound boat. At 3200 - 3400 rpm, we were burning about 10 gph which was
    about 100 - 120 hp into the pump.

    I would start here only because you boat is extremely lightweight. If it does not perform well, cut it to an A2, check it, and so on. B, C cuts are better lower hp V6's
     

  15. sm465np205
    Joined: May 2019
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    sm465np205 Junior Member

    Gonzo so the 6" tall stringers will span from the transom to just in front of the engine where there will be a bulkhead. This bulkhead will serve as the front of the engine compartment. There will be a flat deck from gunwale to gunwale, bulkhead to transom to create the sealed engine compartment. The boat originally had flimsy 3" tall floor supports running the length of the boat. I figured in front of the bulkhead I would use 3" tall rectangle tube or angle in the same location as the old floor supports to allow the floor to go right back in place where it was originally. The only reason I used 6" tall tubing in the stern was so the aluminum motor plates on the engine would intersect with the tubing to mount the engine properly. I think the 6" tubing in the stern and the 3" tubing in the bow combined with gussets to the hulls original transverse ribs creating a grid structure will make for a stout frame to hold the thing together

    Mr efficiency looking at the attached photo doesn't this hull look like a conventional deep vee at the stern? I can't remember the actual angle right off hand. When I was looking at hulls, the majority of these old boats had a similar bow but they flattened out at the stern. If I'm not mistaken these are called warped hulls? I opted to use this hull because it's vee carries all the way to the stern without flattening out at all. I figured I would sacrifice some in draft, but I would potentially gain some stability and avoid cavitation?

    Barry aren't the A2, A3 etc impellers actually larger than the A? Which would lower the peak rpms even further? The A is typically paired with the stock olds 455, Ford 460 or Chevy 454, all of which probably produced a little over 300 HP at 4k some rpms but had much more torque at very low rpms. Seems like I would want to go smaller considering the amount of torque required to turn the A at low speeds?
     

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