Dillon Racing logo Build Your Own Raceboat

Questions from Builders and Prospective Builders
-- Setup Issues --

Actual questions from people who have bought my plans or are thinking of doing so.
The answers I provided for them are occasionally suplimented with some additional (ADD:) information.

Back to Builder Questions

Motors and Horsepower Propellers
Performance

Motors and Horsepower

Shortshaft/Longshaft?
"I've read most, if not all of your information, but I can't determine if your boat uses a 15" or a 20" shaft motor. I've found a 30 Evinrude longshaft which should be perfect if the length is right. By the way it won't be built for racing, just fun."

The boat is intended for short shaft, but a jackplate will allow a long to be used -- or make the motorboard taller to begin with. The motorboard is already 20" high. You might not need to, or want to, jack the motor up as high as we do for racing anyway.

40 hp Pro Tunnel?
"I live here in Surinam, South America. I am very interested in building one of your boats especially the Dillon Pro Tunnel. I can get a 40 hp Tohatsu 2cylinder two stroke outboard here. My question is did you ever run a 40 hp Tohatsu on a Dillon Pro Tunnel?"

No, I have not tried a 40 Tohatsu on the Pro Tunnel. But I am quite sure it can handle it. The Sport C boats that we race with this motor are 11 ft. to 12 ft long, so this is in the range. You will want to be prepared to move the seat forward 6" to 12" if needed for excessive bow lift. Also, the propeller that comes with the motor, and other props Tohatsu offers for this motor, will be useless. Not nearly enough pitch. You will want an 11" to 12" x 18 pitch cleaver. Mercury makes them, but they need to be thinned and trimmed to work. Ron Hill from California USA (http://stores.ebay.com/Ron-Hill-Propellers) makes 11x18 cleavers that should work well, and are probably thinner and trimmed down already.

The transom height on the Pro Tunnel is 20 inches or so. Nevertheless, you will want a short shaft motor for this boat.

You will want to set up a trim system for this boat to control the aerodynamic lift you will experience. I offer some information about that HERE. Or, set up the boat to be driven in the kneeling position so that you can shift body weight as needed. Without some way to control the changes in lift while you drive, a boat like this, at the speeds you can expect with the Tohatsu, can become dangerous very quickly and maybe blow over backward.

Sport C class boats reach top speeds of 58 to 59 mph. It takes a lot of fine tuning of the prop to achieve these speeds. However, Sport C boats are subject to a minimum weight of 675 lbs., boat + motor + driver. A Pro Tunnel would likely be lighter than that: about 230 lbs. for the hull + 100 for hardware (including trim) + 130 for the motor = 460 lbs. A 175 lb. driver makes it 635 lbs. ADD: You may need a little more pitch in your prop -- 19" or 20".

Larger Motor than Recommended -- Mini Vee
"Could I strengthen the mini vee to handle a larger motor if I was to make it longer."

The Mini Vee construction notes suggest doubling the thickness of the coaming near the motorboard. See: HERE. I would suggest doubling it all the way to bulkhead #4. And then add 3/4x2 reinforcements as suggested for the Pro Vee -- HERE. I don't believe you would need thicker plywood on the bottom, but be sure it's got good solid structure backing it up.

You might have to move the seat and dashboard farther forward (as measured from the transom). The positions of these features on the Critchfield should give you some guidance. I know when Critchfield or Lee Craft boats have been raced in our GT classes (25hp-35hp), the seat and dash have to be moved aft 12"-18".

Larger Motor on Mini Vee
"My brother is running a 90 yamaha [on his 13' Critchfield] in the mid 80 mph range. I've got a 70 stinger and 40 tohatsu. Would like to be close to 75 mph."

The Stinger is very much at home on a Critchfield. The 90 must be pushing the limits quite a bit. A Stinger I imagine would be pushing the limits of the Mini Vee. The weight alone would be quite a burden on a boat that doesn't have any real sides.

I had my 2-cylinder 40 Nissan (130 lbs.) on my Mini Vee. Went about 50, but with low water pickup and the right prop there would surely be more there. We run these motors in Sport C and push 60 mph.

Pro Tunnel Horsepower
"I am looking to build a tunnel hull boat and out of all the plans and designs I like the pro tunnel the best. I am not a racer I just like to have fun. My question is would it hold a 60hp short shaft 2 cylinder evinrude cause I have one and wouldn’t mind putting it to use. Or do I need a different power?"

That motor would be too heavy and too much power. Biggest motor I would recommend is a 2-cylinder, 40hp Nissan/Tohatsu. Only 130 pounds and very potent little motor. We use them in Sport C class, and they will push a boat like the Pro Tunnel to nearly 60 mph, with the right prop. ADD: Be prepared to move the seat forward 12" to 18" to accomodate the Tohatsu.

Propellers

Pro Tunnel Prop?
"Do you have any recomendation for a propeller for a Johnson (35hp) for this boat?"

Ron Hill gave our class a few props a couple of years ago -- photos below (click for larger image). The small one was too small, but the others have worked quite well. I don't know if he's made any more. The second photo is a chopper from Ron that I bought this winter (2011) for my Mini Vee. I will also make sure the tunnels get to test it this summer.

You can also do very well with a 17-pitch OMC prop, steel or aluminum, with some cup added to the trailing edge. They don't make these anymore but they show up on Ebay now and then.

I suppose Winrace would have something that would work.

Hill "donor" props
Hill Chopper
Stainless OMC
Hill Cleaver

Cleaver for Pro Tunnel?
"Any ideas of where I can get a good cleaver or racing prop for my 1988 johnson 25-35 hp, surface prop."

Ron Hill in California has worked with us, even gave some props to our GT Pro class (see above). I bought a cleaver from him in 2010 (pic above). A little undersize at about 9.75" diameter (pitch is 17"), and needs more cup, but I had my tunnel (since moved up to Sport C) going 49 mph at 7000-7200 rpm with this prop. I plan to... add a little more cup and whatever else it may need. I think it will work well on my new boat (EZ Tunnel, built in 2011).




Performance

Fastest Design?
"We race 25hp-35 hp mini boats here [New Zealand], what is your fastest hull out of your boat plans?"

Fastest boat is probably the Pro Tunnel with its 42" wide tunnel. The new EZ Tunnel is also fast, but with 40" tunnel probably not quite the potential, especially with 25hp.

Boat Weight?
"Me and my son are thinking about building a speedboat with the possibility of competing in the GT15/GT30 class racing. These classes race with a standard EPA-certified outboard in either 15 (10 to 16 YO) or 30 hp (14 and up)

"The boats are V-bottomed monohulls of minimum 3.5 X 1.3 meters (11.48' X 4.27') with a minimum weight of 210 kg (463 lbs) with a 15 hp and 250 kg (551 lbs) with a 30 hp outboard, full rig including driver.

"Would the Pro Vee be suitable for these classes? I have tried to calculate full weight but I really have a hard time estimating what the added weight to the bare hull will be. All my calculations tend to end up on the heavier side though"

I am currently racing a Mini Vee in our GT Pro class, which has a minimum weight of 650 lbs. Actual weight of my boat, after racing, is about 655 lbs. I carry 45 lbs. of ballast. We also use hydraulic trim in our class -- trim pump, cylinder and associated hardware weigh 20-25 lbs. The battery to run trim and electric start is 17 lbs. My motor weighs 120 lbs., and I weigh 175.

I built this boat with 5mm exterior grade plywood, which weighs about 21 lbs per sheet. 5mm okoume marine plywood is probably slightly lighter. Also, I use a high, double-thick coaming, for minimal driver protection. Lower, single layer coamings could be used if you prefer. Some weight savings could also be realized by using 3mm plywood for the deck.

The Pro Vee is likely to be slightly heavier than the Mini Vee. The Pro is longer and the bottom planking is laminated with two layers of 3mm, which is naturally heavier than a single layer of 5mm. Performance is similar for the Pro Vee and Mini Vee. The Mini Vee is simpler to build.

I have not tried very hard to keep the weight down when building my v-bottoms, because I know they will always be plenty light for our classes. Eliminating ballast, trim, and battery from my boat should reduce overall weight to about 575 lbs. Reducing all possible weight during the building process should be good for another 10 lbs. That's getting pretty close to your 551 limit.

ADD: The latest Mini Vee that I built... weighs 140 lbs. That's a true bare hull, with no finish other than the inaccessable spaces under the deck, and no flotation poured yet.

Pro Tunnel Trim
"...do you need trim and tilt and if so what units do you recommend?"

You don't absolutely need trim but it is highly recommended, both to get the most out of your boat and to keep it under control. The Pro Tunnel is going to generate a lot of lift, especially past 50 mph. A little wind gets under the bow and you'll want to be able to trim down in a hurry.

It is relatively simple to make a trim setup using a cylinder and a pump. I provide some information about that HERE.

Longshaft Disadvantages?
"Hi, im building a Mini Vee, is there any downfall in using a long shaft? I would just build up the transom and use a jack plate for adjustment correct? If you have any suggestions i would apprecaite it."

A couple of our Mini GT racers use longshaft motors (on Mini Vees) without any apparent problems. In fact, rumour has it there's a little more horsepower in a longshaft, something to do with the longer exhaust housing.

Both of these racer's boats have transoms built for shortshaft motors. One of them has an elongated jackplate -- the adjustable part is made five inches taller than the plans call for. The other guy put a taller motorboard on a regular jackplate, reinforcing the board with some steel angle.

Pro Vee Speed?
"I live in Nova Scotia, Canada. We have just started a small racing association. I am currently running a modified duck hunting boat(my design). Raced an older evinruide now I have a early 90’s 25hp Mercury, 10.25x13 prop, and am getting speeds between 34-36 mph. Using your plans what kind of speeds could I expect (I weigh 185)?"

The Mini Vee will go 40-43 with 2-cylinder 25hp Johnson/Evinrude. I weigh 175 and need to carry 20-25 lbs. ballast to make weight -- 600 lbs. including driver.

I don't know how the Merc compares to the OMC performance-wise.

Mini Vee is simpler to build, and maybe a bit more stable than the Pro Vee. I never ran a Pro Vee with 25hp. Ran 45-47 with 35hp, same as Mini Vee.

Pro Vee in Rough Water
"Are the Pro Vee hulls capable of handling choppy waters?"

The Pro Vee is not particularly suited to rough water. The Mini Vee, with its narrower pad, is somewhat better.

Pro Vee vs. Critchfield
"I am looking at the Pro Vee boat plans. I'm not planning on racing this other than in the river. My brother has a 13 ft Critchfield. How would this boat compare?"

I believe the Pro Vee would compare very well, and in particular would be quite a bit lighter -- maybe by 100 lbs. if the examples I've known are typical. Barehull weight for either of my v-bottoms will be 180 lbs. or less.

The Mini Vee is also a good-performing boat, and will do quite well against the Critchfield.

Mini Vee vs. Super Spartan
"I am considering building a Mini Vee. This will be my first boat built and I am looking forward to getting started. My other option would be a Glen-L Super Spartan. If you could help me decide I would be very thankful. I am not going to be doing organized racing but I do want my boat to be fast and agile. I want it to do at least forty mph"

For flat-out speed you will likely do better with the Spartan. But hydroplanes are not known to be agile. You can see them in races taking very wide turns, while v-bottoms will turn quite tightly, only out-turned by the tunnelboats.

The Mini Vee runs 40-42 mph with a 25hp OMC (Mini GT class), and 45-47 mph with a 30-35hp OMC (GT Pro class). Both of these classes are subject to minimum weights, so your rig will likely be lighter (I'm about 175 lbs. and need 50 lbs. ballast to make weight) and therefore a bit faster, and certainly quicker.

In a hydro you will be driving on your knees. In the Mini Vee you'll be comfortably settled in a seat (plans available) controling your throttle with your foot. Oh, you can put a seat in a hydro, but they are really meant to be controlled, partially, by the shifting weight of the driver.

Back to Builder Questions



        View Cart

          HOME

BUILD A RACEBOAT
  • Tunnelboats
  • V-bottoms
  • Jackplate Plans
  • Cockpit Plans
  • Seat Plans
  • My Customer's Projects
  • Bob's Projects
  • Start YOUR Project Today!

    CONTACT
    HELP!
    About Bob

           
Send a Link to a Friend


  • POWERBOAT RACING
  • Mini GT
  • GT Pro
  • Sport C
  • Boats For Sale
  • VIDEO



    Sitemap