Marine Specialties, P. O. Box 19094, Houston, TX 77224-9094
(713) 468-6070 Phone (713) 468-6072 Fax
Frequently Asked Questions
Who is Marine Specialties ?
What is the Best Gasoline Engine ?
What the Zenoah G-42 "is" and "is not"
The More RPM the Faster I Go, Right ?
Propeller Sizing, What is Right for My Boat ?
So How Do I Make My Boat Go Fast ?
Propellers: 2 Blade, 3 Blade or More ?
One Rudder or Two ?
Why Use the Marine Specialties Double Rudder Outdrive ?
Bearings, Bushings or What ? Not available at this time.
Two Cycle Performance Basics, Stroke, Bore, etc. Not available at this time.
Gasoline: Regular or Premium ?
What Oil and How Much ?
My Engine Won't Run, What's Wrong ?
Are All Zenoah G-23's the Same: Compact, Sub-Compact, Super Sub-Compact, Penut, etc. ?
WHO IS MARINE SPECIALTIES ?
Marine Specialties has been in continuous operation producing the highest possible quality model boating products since the 1960's. We became involved in gasoline boating in the early 80's with the advent of the Echo weedeaters. We run what we sell and sell what we run (with the exception of a few personal race motors)! We do not reinvent the wheel or copy competitors products. If a product exists that works well, we use it and distribute it such as: Dumas boats, Aeromarine boats, Prather boats and Stainless Propellers, Sullivan and DuBro products, Futaba and Hitec radio gear, Homelite, Zenoah, McCulloch, Echo, J&G and Quickdraw motors and much more. If we see a need for a product, we design, test, manufacture and market it. Marine Specialties "Pro Series" products are no-excuse premium products that will help create a lighter, faster more reliable and easier to service boat project. Marine Specialties "Sport Series" products are cost competitive products that will be attractive to a budget conscious boater who is less concerned with all out performance. We always listen to our customer's wants and needs and recommend the product that best suits their particular project.
WHAT IS THE "BEST" GASOLINE ENGINE ?
There isn't one, but we will tell you our opinion based on our experiences and observations. We currently own, run and have dynoed the following: 21-24cc Echo, 21, 25, 28 & 32cc McCulloch, 22.5cc Zenoah G2D, G23LH, G23L, G23PUM, 22.5 & 25.6cc J&G top end and billet motor, 25 & 30cc Homelite, MS35 Equalizer, 36cc Quickdraw A4P Decked, MS 42cc Zenoah Compact, MS 60cc 2X Outlaw, 30cc Cobra/Enforcer/Prather.
Most "bang for the buck"….. Zenoah G230 PUM or G23 as it is commonly known. Stock with a canister muffler it will perform the same as a ($400 to $500) "Killer" Homelite with tuned pipe. With standard modifications (raised compression, larger exhaust and intake timing and a tuned pipe) the G23 performs better yet. Price for a ready to install Zenoah G23 package can range from $350 to $900 depending on options and modifications.
For the cheapest "starter" or "play" boat the Homelite is the right motor. If you are resourceful and inclined to scrounge you can get one for $5 or less or a trunk full for about $20. This will almost undoubtedly be 25cc direct drive model. We recommend the 30cc with clutch, but it is unlikely that you will find this model as "junk". We sell this motor new for $149.75 or ready to install super stock (big bore carburetor, straight pull intake manifold, throttle linkage and pro series mounts) for $249.75. You can spend much more on a Homelite with modifications and accessories by Marine Specialties or others, but we try to encourage those willing and able to spend more to invest in the Zenoah G-23. We feel they will be happier overall due to the G-23's much smaller size, lighter weight, better longevity and greater horsepower.
MARINE SPECIALTIES ZENOAH G-42 … WHAT IT IS NOT !
It is not a modified water cooled airplane engine. The G-38, G-45 and G-62 airplane engines all utilize an angled spark plug style cylinder which is not suitable for proper water cooling. Many have tried to use these as well as the Echo and other angled plug engines. The water jacket is usually/typically installed on the cylinder wall only, not the combustion chamber which is where the majority of the heat is concentrated. Furthermore angle plug combustion chambers are inherently non-hemispherical resulting in lower compression, less efficiency and lower power.
Why 42cc? It is the largest size engine that can be utilized direct drive (1 to 1 ratio) with commonly available reasonably priced propellers. Marine Specialties manufactures a 60cc engine with a 2 to 1 speed up drive, 12,000 engine RPM with a 24,000 propeller RPM. The cost, complexity and size of this type of set up has proven to be unjustifiable on engines smaller than 60cc.
It is not recognized as a legal size racing engine. National sanctioning bodies (IMPBA and NAMBA) have limited gas engines to a maximum displacement of 36cc's. We have been told by several people that they are racing our 42cc engines in "Open Gas" but that is on a local club by club basis.
It is not a G23 hop up. The Marine Specialties G-42 is a G-23 on steroids. Larger cases, crank, rod, piston, cylinder, carburetor and exhaust. The only parts interchangeable with the G-23 are the ignition and sparkplug. Both the G-23 and G-42 mount in 5" rails and are interchangeable in a boat.
It is not a "large boat only" engine. We currently have one installed in an Aeromarine 43" Challenger (the spark plug only sticks out of the cowling 1/4") and our standard R&D test boat is a 50" Apache. The G-42 is both smaller and lighter than a Homelite 25 or 30cc. With stage 1 modifications the G-42 will produce on the water RPM's equal to the Quickdraw A4P, but will have a much broader and more useful torque curve and power band. Stage 2 modifications produce much higher on the water RPM than the Quickdraw A4P in our test boat (Aeromarine 50" Apache).
The Zenoah G-42 is not "getting to big too big to package into a boat". It's physical size and weight is larger than the Zenoah G-23 but smaller than both the Homelite and Quickdraw A4P. Below are some basic measurements of the three mentioned engines. If you feel these are in error please contact us as we try to keep this data as accurate as possible. For a more complete chart see enginesizeweight.htm
Weight (lb) Width (in)
with mounts & collet Ex. port to
no exhaust Height (in) Length (in) carb. face
Zenoah G-23 3.74 6.3 7.8 4.4
Zenoah G-42 5.65 7.7 8.4 5.3
Quickdraw A4P 7.83 8.0 9.1 4.4
Homelite 30cc 6.08 8.3 10.2 4.5
It is not expensive. The stage 1 package costs $1099.75 + 7.50 shipping and handling (in US). This includes the G-42 compact with pro series four point vertical access rubber isolated mounts, Stage 1 modifications, choice of square drive or collet, straight pull carburetor linkage and nickel plated steel tuned pipe with silencer. Yes, more expensive than a stock G-23 or Homelite with an aluminum pipe ($300 to $500). A little more expensive than a fully modified G-23 or J&G with the QD steel pipe ($700 to $1000). The same price as a Quickdraw A4P or Mathe with steel pipe. And much cheaper than a Quickdraw multi cylinder ($1800 and up). Expensive or cheap all depends on your point of reference. Remember, speed costs money…. Just how fast do you want to go ?
MARINE SPECIALTIES ZENOAH G-42 …. WHAT IT IS !
It is a custom manufactured engine, specifically for model boat use, by Marine Specialties. It uses mostly Zenoah industrial engine parts (as does the G-23) but all of the components with a few exceptions are modified for this purpose. It is a durable and economical engine to own and operate once purchased. It, like the G-23, has a low inertia crank providing excellent throttle response and making it unlikely to hydraulic. Marine Specialties has priced all replacement parts for the G-42 within 20% of the prices for the G-23 parts. It requires no special oils or operating procedures - just like the G-23.
It has the same bore and stroke relationship and factory port geometry as the G-23 with 82% more displacement. It produces over twice the horsepower of a G-23, this is due to the reduction in percentage of parasitic horsepower loss to the ignition, bearings and windage. Zenoah specifies that the stock G-23 is 2 Hp at 10,500 RPM and the stock G-42 is 4.25 Hp at 8,500 RPM. We have found this ratio to be accurate for the stage 1 and stage 2 modifications as well.
The G-42 is designed to fit in standard 5" rails and can be installed in a 43" Challenger with only 1/4" of the spark plug cap protruding. It is a direct swap for the Marine Specialties G-23 installation if a Marine Specialties straight pull linkage and steel tuned pipe are installed. This swap takes less than 10 minutes.
GENERAL INFORMATION
Our personal test bed is a 50" Apache. In all cases a Prather stainless steel 275 prop seemed to work best thus making on the water RPM comparisons easy. RPM was recorded with onboard tachometer and runs were conducted in a manner to eliminate cavitation errors. Marine Specialties super stock Homelite 30cc with big bore carburetor, straight pull intake manifold and modified canister muffler ran 11,700 RPM. Homelite 30cc super modified by XXXX with tuned pipe ran 12,400 RPM. Zenoah G-23 with canister (helicopter) muffler ran 12,400 RPM. Zenoah G-23 modified by XXXX with o-ring style aluminum tuned pipe ran 13,000 to 13,500 RPM. Zenoah G-23 with Marine Specialties Stage 2 modifications and steel tuned pipe ran 14,500 RPM. Quickdraw 35cc A4P decked with QD new pipe, no silencer, 15,000 RPM. Marine Specialties Zenoah G-42, stage 2 modifications, with MS nickel plated steel tuned pipe and silencer ran 16,800 RPM.
WHY STEEL TUNED PIPES ?
They work the best, just examine any dirt bike or racing go-kart ever made. They will have a steel exhaust flange and expansion chamber and if using a silencer it will typically have an aluminum silencer body with a steel core. Aluminum chambers (tuned pipes) work OK on nitro engines where exhaust gas temperatures are quite low, but with the much higher EGT's of gasoline engines the aluminum chambers do not resonate properly thus dramatically reducing there effectiveness. The many aluminum exhaust systems available from Marine Specialties and others are lightweight, look good and offer various header tube configurations for versatile and easy installation as well as being less expensive than the Marine Specialties nickel plated steel exhaust system and the steel systems manufactured by others. On the dyno, the worst steel tuned pipe will produce much more power than the best performing aluminum pipe. All this being said, there is no "best" exhaust system, just like there is no "best" engine, it is dependent on the particular requirements. Each builder must decide which factors are most important on their project to select the type and model exhaust system which will best satisfy their requirements. Here at Marine Specialties we sell aluminum tuned pipes 4 to 1 over steel tuned pipe systems, this is primarily due to $$$$.
WHAT PROPELLER ?
There are many good propellers available from several manufacturers. In our experience the most popular propellers for gasoline applications are the Prather propellers, Octura X series and some 14, 15, 16, 19, 21 and 22 series and the V967/3, some ABC and Prop Shop propellers. We personally use the Prather Stainless steel propellers almost exclusively, specifically the 265, 270, 275 and 280 sizes due to their almost indestructible strength, good performance, good looks, economical price and ready availability. All of Marine Specialties engines are designed to work well with the commonly available economically priced propellers previously mentioned. There is no need for the exotic multi-blade custom built propellers that are necessary to fully utilize the output of engines with high torque at low RPM or low Torque at very high RPM.
CLOSING
We hope this information has been helpful in answering your questions about the Marine Specialties Zenoah G-42 Compact as well as addressing several commonly asked questions about gas boating in general. If anyone needs more information about any of the products we manufacture or distribute please feel free to contact us by phone at 713-468-6070 Mon.-Sat. 9:00am - 5:00pm central standard time or Fax 713-468-6072.
The more RPM I turn the faster I go, right?
Not always! Unloaded or advertised RPM mean absolutely nothing without knowing what prop they will turn on your boat. A torque value at claimed RPM would be very helpful, but to get this one would need to have a real dynamometer, and very very few companies have and use one in their engine development work. There are no reasonably priced commercially available brakes available that meet our requirements (20 ft lbs at 6,000 RPM and 0.1 ft lbs at 25,000 RPM as well as the ability to absorb 10 horsepower continuous input) and inertia type dynamometers are not suitable because we have found that measurements recorded before the engine and pipe are fully heat soaked are meaningless. If torque were given for the claimed RPM you would know the horsepower by
Horsepower = Torque (ft*lbs) x RPM / 5252
How hard is it to turn more RPM? Actually it is quite hard. Drag increases as a function of velocity squared, for instance it will take 4 times the power to spin the drive line and prop only twice as fast. This also applies to moving a vehicle through the air but a boat complicates this by moving through the air and water at the same time. The aerodynamic drag of a boat will increase as a function of velocity squared but the hydrodynamic drag will usually decrease some as the boat "airs out" or "loosens up" with greater speed thus explaining why a "loose" mono or properly trimmed hydro will run at faster speeds than a "wet" , more stable set up. All of this means you need an engine that not only produces maximum possible horsepower per size/weight but also has a broad enough torque curve/power band to accelerate the boat through the portion of the hulls total drag profile (aerodynamic & hydrodynamic) where drag is at a maximum. A catamaran or tunnel style hull also has a wake affect between the hulls which results in a flooding of the propeller further increasing power demands in this lower speed range.
THE BIGGER THE PROPELLER I RUN THE FASTER I GO, RIGHT ?
Not necessarily. It is very easy to over prop a gas boat. In the past it was assumed that gas engines turned slow (about 8,000 RPM) with substantial torque and thus required the largest available propeller (about 80mm). This may have been true in the past, but current gas boat engines are no longer just "weedeaters" in a boat. The most high performance engines can lose almost half of their horsepower by being operated as little as 1,000 RPM above or below their power peak thus making propeller selection and boat set up quite critical. Propeller location and thus efficiency also affects what size propeller works best on a given boat. On record setting submerged drive boats you will note propellers as small as 60mm with Zenoah G-23 engines. These boats will be light (9-13 lbs) and the submerged drive offers highest efficiency.
2 BLADE, 3 BLADE OR MORE?
Usually a 2 blade propeller will offer best performance. The two variables on propellers are diameter (push) and pitch (speed). To select a propeller for your boat you need to first determine the smallest diameter propeller that will push your boat without cavitation or excessive "slip". Once the propeller diameter is selected you want to absorb all additional horsepower with increased pitch thus maximizing speed. So how does a 3rd or even 4th blade help? It does not increase diameter, and it does not increase pitch, but it (they) will increase drag (not good). So why are they made? On full size boats with 800 to 1,200 horsepower per drive propeller, maximum diameters are limited by the cavitation plate, outdrive and propeller tip speeds, so to absorb the power, "diameter" is artificially increased by adding more blades. On RC boats 3 blade propellers are most prevalent on outboards (which have diameter limiting cavitation plates just like the full size units). On a gas boat a 3 or more blade propeller will offer smoother power delivery which will usually decrease "squirrelieness" but for maximum efficiency and performance where diameter is not limited a 2 blade propeller is usually the best choice. They are also easier to sharpen, balance, polish, available in more sizes and styles, lighter and cheaper.
SO HOW DO I MAKE MY BOAT GO FAST?
The same as any other successful racing effort, with lots of time and or money. The quickest easiest way to go fast is to buy something that is already going fast, but beware, just because you buy a boat that was the fastest one day does not in any way guarantee its propeller and setup will produce even an average performance on a different pond with different weather and water conditions, (so you should buy the whole team just like NASCAR). To go fast you will need the most usable horsepower your engine can produce. (Useable means that your engines torque curve is well matched for your hull drag profile.) This is most easily accomplished on a dynamometer (money $$$$$). This allows you to very accurately record the affects of varying squish band (compression), exhaust timing, intake timing, blow down angle (angle between exhaust and transfer port opening) and scavenging (port sizes, angle and locations). Each time a new cylinder configuration is tested all the "tunables" need to be reoptimized, exhaust size and length, carburetor size and intake length and ignition timing and advance curve (time). Once the engine has been optimized for your application and installed in the hull of choice you are ready to test propellers. You will need a good selection of propellers in various sizes and styles (money $$) to find out what your boat works best with. Each propeller must be balanced, sharpened and modified as necessary (time). Now it is time to go to the pond (fun), but first you will need an onboard recording tachometer (money $) or a telemetry system (much more money $$$) and a speedometer (cheap) or a radar gun (beg, borrow or buy $$$$). A note on radar guns, not all are created equal for use with small non-metallic objects moving across water and generating a spray. A tripod mount will give more accurate readings than hand held and unless your readings are very consistent they are probably useless. Now, with each propeller you have, run the boat until the setup produces a stable ride, no pitching or rolling, with the minimum amount of hull touching the water and the onboard tachometer or telemetry system showing the engine operating at exactly the maximum power RPM (time). Record the speed and RPM of each run. The fastest speed would be your best choice for a straight line propeller for the conditions you tested in. If you wish to heat race or want the best "all around" propeller you would need to use telemetry to record in real time the RPM of the engine in a maximum rate (minimum radius) turn. This RPM should be at or slightly above the torque peak RPM for your motor setup. (Torque peak RPM is always lower than power peak RPM and maximum useable power is found in this region.) Don’t rest yet, to turn in a "pro" performances every time this entire procedure needs to be done for every different body of water you intend to run on under the various weather and water conditions that exist when you run. Obviously only a few if any boaters have the time and ability to go to this level of preparation. Satisfactory performance is most often achieved by using a "tried and true" basic set up improved through simple trial and error experimentation. A few things to remember, Newton’s first law – for every action there is an equal and opposite reaction. Roostertails might look neat, but the water thrown way up in the air by your propeller will push your boat down, not forward. The fastest boats typically have long low roostertails. Play boats that produce a steep roostertail (45 degrees or greater) are operating at very low efficiencies (explaining the large propellers on less powerful engines) and would probably benefit in both performance and handling by going to a "proper" set up. The most common mistakes seen on transom exit surface drive boats are using a stuffing tube and or drive that does not allow the flex cable to exit the hull low enough (the centerline of the flex cable should never be more than 3/16" from the lowest point on the keel, any more than this and the performance will likely suffer) and using a drive system that does not allow independent adjustment of prop shaft angle and prop shaft depth.
ONE RUDDER OR TWO?
In most cases a dual rudder set up will give maximum performance. The most common gas boat set up is a surface driven, V-bottom mono, so lets look at this case. As the boat runs faster and faster you will notice less and less hull in the water which reduces "inherent" stability, also to run faster greater and greater amounts of power are required which when the "power hits the water" is an increasing destabilizing force. The rudder(s) serve two purposes, one, to stabilize the hull in a straight line by counteracting propeller forces and two, to turn the hull for maneuvering. In the mono setup, with the typical right hand offset single rudder, as the hull rises up on the keel or even out of the water a very small percentage of the rudder remains in the water to counteract the increasing instability. See figure 1 To increase straight line stability "turn fins" are now typically added, and with them comes increased weight and drag. Now, when it comes time to turn, the turn fins are trying to make the boat go straight and the rudder is trying to make the boat turn. This results in a great increase in drag (like opening a parachute) (see figure 2) resulting in slower corner speeds. By using dual rudders both surfaces contribute to both straight line stability and cornering (see figure 3) allowing smaller surfaces which create less drag and result in more speed. A single central rudder shares some of the benefits but will usually need to be quite a bit larger, (higher servo force and linkage requirements) make propeller changes more difficult and interrupts the spiraling propeller wash decreasing drive efficiency. (see figure 4 & 5) The dual rudders also offer more protection from propeller injuries.
WHY USE MARINE SPECIALTIES HBR DUAL RUDDER OUTDRIVE?
Quality and design. Strut angle and depth as well as rudder pivot angle are crucial to good boat performance. Once optimum settings are obtained you want them to stay put. Marine Specialties hardware secures these critical parts with two fine thread (#8-32) fasteners instead of the more common practice of one coarse thread (1/4-20) fastener. This results in much higher clamping pressure, holding critical adjustments secure during the most severe use. Also, Marine Specialties’ safety shear rudder feature allows the rudder blade to swing free, after shearing a shear pin, leaving the rudder pivot block and steering linkage unaffected, thus maintaining the critical rudder pivot angle adjustment. Most other designs "break away" by rotating the entire rudder and pivot block about their single mounting bolt which will upset or destroy the steering linkage and rudder pivot angle adjustment.
PRESSURE CAST PARTS, WHATS THAT ?
Most all of Marine Specialties parts are manufactured by pressure casting. This process injects molten aluminum into heavy steal dies at 6,000 psi. The permanent steel tooling ensures dimensional consistency, and the pressure reduces voids and increases part density, thus producing the most consistent high quality parts possible.
BEARINGS, BUSHINGS OR WHAT?
TWO CYCLE PERFORMANCE BASICS, STROKE BORE COMPARISON.
GASOLINE – REGULAR OR PREMIUM?
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Marine Specialties
P.O. Box 19094
Houston, TX 77224-9094
713-468-6070 Phone
713-468-6072 Fax
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