Starcraft Holiday senior project: Convert to twin Jetski drives

[drev500]

Starcraft Titling/Custom boat

My title is a bit vague but I was hoping someone could answer a question for me or give me some advise.

I recently acquired an 18ft Starcraft Holiday. It is titled (supposedly) but I am waiting on getting it from the original owner. According to the hull sticker, the last time it was registered was in 1975... the hull is in excellent shape but the interior is shot (was never covered).

I bought the boat for a school project. I am in my senior year studying mechanical engineering and I wanted to design a jet boat using jet drives from a pair of jet skis. The jet skis are a pair of 110 hp engines that will provide the forward thrust. I know these boats are only designed for 120hp (according to the USCG plate on the boat) but jet pumps are axial flow propulsion units that transmit the forward thrust in a horizontal line. This thrust is transmitted to the hull which is capable of withstanding much more power than the transom mounted Outboard than it came with.

So, with my new design, I will be exceeding the hull rated hp and also be using a different propulsion setup. Does this make the title/ USCG plate with the serial number void? If so, I how do I go about getting a new registration for it? I have found the USCG builders workbook but I would like to use the original title if possible but I am having trouble finding anything about repowering/hp ratings.

This is my first boat build so pardon my ignorance.

Thanks for the help! I will start a thread once the design and build starts. Figured everyone would enjoy it. Hopefully no one will be upset with my cutting

 

[Bondo]

So, with my new design, I will be exceeding the hull rated hp and also be using a different propulsion setup. Does this make the title/ USCG plate with the serial number void?

Welcome Aboard,..... Nope,.... You are not a manufacturer, yer just refittin' the existin' hull,....

Btw,.... I'm guessin' yer gonna be disappointed with the final product,.... but good luck with it anyways,....

 

[jbcurt00]

Is your Holiday an outboard or I/O model? Hopefully the I/O, and its an 18ftr?

Good luck,

 

[drev500]

Welcome Aboard,..... Nope,.... You are not a manufacturer, yer just refittin' the existin' hull,....

Btw,.... I'm guessin' yer gonna be disappointed with the final product,.... but good luck with it anyways,....

What makes you think I'll be disappointed? If you have experience with such a thing, I would love your input.

 

[Bayou Dave]

You really should have gotten the title when you bought the boat.

 

[Frank Acampora]

The title does not prohibit you from making modifications to the hull, just as titling an automobile does not prohibit changing engines to a much larger one or chopping and channeling the body.

HOWEVER: Once you put the jet-ski engines and drives into the hull it becomes an inboard which is exempt from horsepower limitations. Again, you must change the title and registration to show that the hull is now an inboard. Probably register it as a home built.

By disappointed, Bondo probably thought (and rightly so) that the hull will not perform nearly as well as a single jet ski and even with the extra horsepower it will not deliver close to what a 200 horsepower outboard will deliver in top speed. Acceleration, though should be very exciting.

AS an example: I know of a jet boat that is only 16 feet long. It is powered with a Chevy 350 with two four barrels, putting out well over 200 horsepower. Top speed is only about 60. My 14 foot flat bottom with a 125 outboard tops out at 55

because of the nature of a jet drive, the boat is always moving away from the water column and thrust. For a given jet drive, the faster you go the less thrust you have no matter how much horsepower (within reason) you put to it.

 

[drev500]

The title does not prohibit you from making modifications to the hull, just as titling an automobile does not prohibit changing engines to a much larger one or chopping and channeling the body.

HOWEVER: Once you put the jet-ski engines and drives into the hull it becomes an inboard which is exempt from horsepower limitations. Again, you must change the title and registration to show that the hull is now an inboard. Probably register it as a home built.

By disappointed, Bondo probably thought (and rightly so) that the hull will not perform nearly as well as a single jet ski and even with the extra horsepower it will not deliver close to what a 200 horsepower outboard will deliver in top speed. Acceleration, though should be very exciting.

AS an example: I know of a jet boat that is only 16 feet long. It is powered with a Chevy 350 with two four barrels, putting out well over 200 horsepower. Top speed is only about 60. My 14 foot flat bottom with a 125 outboard tops out at 55

because of the nature of a jet drive, the boat is always moving away from the water column and thrust. For a given jet drive, the faster you go the less thrust you have no matter how much horsepower (within reason) you put to it.

Thank you Frank for your response.

I understand the top speed limitations and I am not really concerned about doing 60mph. This is my first boat so I am not interested in hitting speed records. I am more concerned about having power and acceleration.

The idea of the boat is to not have any drive system lower than the hull of the boat to allow an easy pass over a water obstruction (log) that would damage a boats prop. Its not a new idea but retrofitting jet ski drives into a Starcraft is which is why I wanted to take on the project. I am very appreciative for any other ideas or insight you are able to give me that would allow me to better the project.

The title on the other hand is available. I will ask the dmv how to go through the process of titling it as an inboard.

Thank you

 

[jbcurt00]

Is your Holiday an outboard or I/O model? Hopefully the I/O, and its an 18ftr?

Good luck,

I/O or OB?

 

[drev500]

I/O or OB?

Sorry JB.

It is an outboard. I am redesignin the transom. I will be removing what is there already and adding a solid aluminum plate. It will be reinforced so a swim platform can be accepted. I do not want any wood on the transom so the plate will be substantial.

The splash well will be removed also because the engine compartment will be extended as the inboard jets are longer. This does move the CG (center of gravity) but I will be balancing it out with a fuel tank(s). If room/budget permits, I would like one tank running along the keel. I am taking the ski motors/pumps out this weekend to be able to make some measurements so designs can be made for engine/pump location and the transom.

 

[drev500]

It is also 18 feet.

 

[Bondo]

Again, you must change the title and registration to show that the hull is now an inboard. Probably register it as a home built.

Ayuh,.... This must vary by state,.... Here in NY, as well as in Maine, the title follows the original hull, regardless what ya do to the hull,....

Change from I/O to outboard, to a paddle, the title follows the hull, no new title necessary,....

so designs can be made for engine/pump location and the transom.

The transom does nothin' but hold the water outa the hull, with a jet-drive, no big heavy plate needed,....

Takin' out the splashwell, ya gotta add more Structure to replace the strength, 'n support removed with the splashwell,....
Boxes, curves, 'n bends in thinner sheet material is better than heavy plate,...

As to my comment, I've seen alota attempts at puttin' jet-ski drives into various hulls, from canoes to cruisers,....

Few to none were deemed "Successful",.....

Jets need good clean water flow under the hull, feedin' the intakes, shoe adjustments become Critical,....
Ole riveted hull Starcrafts just Don't supply clean water flows, the rivets create turbulence,...

But, Hey,.... Yer young, 'n seem Ambitious,... Go for it, 'n learn from it,......

We'll be here to help out later,...

 

[jbcurt00]

Is the hull even marginally flat across the bottom of the transom....

I'm on my phone, but IIRC, most 18ftrs had a V shape to the stern end of the hull. And some had whats often called a Gullwing hull at the stern....

Concave/convex hull is what I seem to remeber Starcraft calling it.

Pix of what your whole rig, and a shot of the stern wpuld be helpful....

Good luck

 

[drev500]

Bondo, I understand the transom plays little in structural with a jet as forward thrust is not applied to that section of the boat. I am just worried about the swim platform. I haven't done any calculations but will shortly and see what I need. I am also still in my research stage so I am trying to learn as much as possible. Also, I have seen the many that fail and have seen why. Most flat bottom boats (jon boats in particular) induce lots of air under the hull. This air creates cavitation issues with the pump. Water pumps like pump water, not air. Also, they have strakes and other hull features in front of the intake which again induce cavitation. With the Hoilday I am using, the hull is a v bottom which will provide for the needed ventilation of air that passes under hull and will bleed it off before the intake (hopefully). There are some things that can be done if cavitation still occurs but I wont know till a water trial to see if it is. Keeping the pumps as close to the keel is a key. This will provide the pumps with the most water. I appreciate your encouragement and look forward to the project. This will be a fun project as mush as it will be a learning experience. It will challenge my teammates and I which excites me. I really appreciate your help!

JB,

This hull has a v at the transom. Does not curve like the ones you are talking about (I have seen them and is why I chose the Starcraft Holiday). The v is slight, maybe a 12 degree deadrise (haven't measured it). From what I have gathered, people have said that the minimum deadrise for a jet is 10 degrees. I am hoping th actual deadrise is larger than this. I will get back to you with a picture and a calculated dead rise. Thank you!

 

[Frank Acampora]

Remember: Your jet pumps are coming out of a VEE hull, thus they have deadrise on each side of center or there is a flat mounting flange with a VEE adapter. When mounting side by side in a VEE hull you will need to make adapters for the inlets to match the angle of the hull. Not an insurmountable problem, you just need to know beforehand and allow for it.

 

[drev500]

No Title

Remember: Your jet pumps are coming out of a VEE hull, thus they have deadrise on each side of center or there is a flat mounting flange with a VEE adapter. When mounting side by side in a VEE hull you will need to make adapters for the inlets to match the angle of the hull. Not an insurmountable problem, you just need to know beforehand and allow for it.

Frank, thanks for pointing that out. I chose this jet skis for that reason. The jet intake actually unbolts from the hull unlike seadoo jet intakes where they are molded into the hull. They are flat so mounting is simplified

 

[drev500]

For people just joining, there are three threads merged into this one. This is project my team and I are taking on for our senior year design in engineering at the University of Cincinnati. Building a twin drive Starcraft Holiday. We will comment as much s possible and plan to include many pictures so please, join us in our adventure. We greatly appreciate any participation from the fellow members. Thanks for looking!

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Hey guys,

I am looking for floor opinions. So some of you may know but I am a senior studying Mechanical Engineering. I am building a jet boat with a Starcraft Holiday.

Well in the meantime of us finishing the designs, I want to put a new floor in it to help settle my nerves and make me feel better. This is a school project so I can't break the bank but I want to do a floor that will last for some time. I plan on using exterior wood, sand it and coat it with polyester resin. I can't afford the epoxy or marine grade wood at Menards ($80 a sheet). The bottom side and edges will be coated with resin and the top side will be coated and layered with a layer of mat.

I want to paint it and have thought about using garage floor paint. Seems people have had some good experiences with it and its not terrible priced. Is this a bad idea? Also, could I just coat the wood with the floor paint (if its a good idea) and avoid the fiberglass or go overkill and do both? I would prep the floor after the fiberglass with some sanding and cleaning then coat.

I am after a non skid surface that is also a little rubbery. I was thinking of some Rustolem Bed Liner but with it being black, that floor would be HOT!

Oh, one thing to add, the wood would be 3/4". Thanks!

P.S. I will start a thread soon once we get the thing rolling.

 

[drev500]

BTW, not a single dent under the hull or loose rivets. The last time the boat was registered (according the hull tag) was in 1975. The bottom side paint is has no scratches in it and I had some water it, not a single drop. Pretty lucky to find something in this condition. I am wanting to bring new life into her so I will be asking a lot of questions as this is my first resto/repower.

thanks,
Evan

 

[Woodonglass]

What are you going to use for power???

 

[drev500]

What are you going to use for power???

A pair of Yamaha jet ski's. The idea is to create a boat that will sustain little to no damage to the vessel and the drive system in the event of a log strike (at reasonable speeds). I am on the Ohio River and this past year we had a lot of drift. We never had a strike but a guy down the way from friend's place sank his 26' go fast. Hit a log doing 50mph in the middle of night and well, the lower drive separated from the transom. The boat floated for maybe 15 seconds...

So it got me thinking, I need a project for my Senior year to show case what I have learned. I haven't seen anything like this done on a Starcraft so I figured lets do it. Found this beauty for 800 and sold the outboard for 200 (I wanted it gone quickly). Picked up a pair of Yamaha's and now we are designing. Finally got the boat all modeled in Solidworks...that was an interesting task with no drawings to go off. Tried asking Starcraft if they had anything but their database didn't have anything. I was able to get an old brochure but that's it. We used a tape measure and plumb-bob to get as close as we could to dimensions. When all said and done, I get to have a toy to play with after I graduate

 

[jbcurt00]

How about we make this THE topic about this project, and when you're ready, just add to it?

I can merge your other 2 topics into this one, that way everybody can see where you started and where you're headed.

Hows that sound?

I can change the title to something along the lines of:

Starcraft senior project: Convert to twin Jetski drives

Does SolidWorks allow you to output images in multiple formats? If so, start a photobucket.com account, upload the pix there and paste the IMG code into your posts.