Motor to catamaran: how to choose, install and operate without errors

The catamaran is not just a boat, but a whole philosophy of water recreation: stability on the wave, space for passengers and cargo, the ability to equip a powerful engine without the risk of overturning. catamaran-engine It's a much more complex task than a normal PVC boat or an aluminum drifter, and it's expensive to make mistakes, from speed loss to fuel overruns to a lot of things like that. transmutation Or even a boat tipping over.

In this article, we will discuss selection criteria From the calculation of the minimum power to the nuances of installing an outboard motor on a two-hull vessel. quirkyIt's a problem that causes premature engine wear and tear or an accident, and you'll also find out why. electric motors Catamarans are becoming more popular, despite the high price, and how to save on fuel without losing dynamics.

Spoiler: Yamaha F25 or Mercury 40 ELPT - Not always the best choice, even if they are praised in the forums. catamaranIts length and your tasks: fishing on the lake, high-speed walks on the river or long sea crossings.

1. Why a catamaran needs a special approach to choosing a motor

The main problem is that load-sharingUnlike a single-hull boat, where the motor is attached to a transom and the load is transferred to one hull, the catamaran has a unique power. two-hullAnd that creates additional moments of power that can lead to:

• 🔹 transom deformations If the engine is too heavy or the mounting is incorrect.
• 🔹 Loss of manageability - with the wrong choice of height of the lower unit or the angle of inclination of the engine.
• 🔹 Fuel overruns - due to increased water resistance (catamarans are wider than conventional boats).

For example, catamaran 4 meters long motorized Tohatsu M18 18 hp can perform worse than a PVC boat of the same length with the same engine. sail-laden And the resistance of the two hulls. minimum capacity For catamarans, the reserve is calculated with a margin of +20-30% compared to single-hull vessels.

⚠️ Attention: If you install the engine on a homemade catamaran of barrels or PVC pontoons, Check the strength of the transom. It's a bend, even a light one. Honda BF5 (5 hp) can deform the mount over time due to vibrations.

Another nuance. transmessIn catamarans, it is often higher than the standard 381 mm (15 inches), which requires use of the silk. long-dadewood (Extra Long Shaft) or special adapters. Ignoring this rule leads to screw-cavitation and loss of traction.

2. How to calculate the optimal power of the motor

The formula is simple, but with amendments: Minimum power (hp) = (length of catamaran in meters × 2) + 10% - for calm water bodies. For the sea or major rivers: Multiply the result by 1.5.

Examples of calculations:

Catamaran length	Lake/river (calm)	Sea/large river (wave)	Recommended models
3.5 m	8-10 hp.	12-15 hp.	Mercury 9.9, Suzuki DF15
4.2 m	12-15 hp.	18-20 hp.	Yamaha F20, Tohatsu M20
5 m or more	20-25 hp	30-40 hp	Honda BF30, Evinrude E-TEC 40

However, Paper figures and real dynamics They often don't match. Here's another thing to consider:

• 🛶 Weight of passengers and cargo: Each +100 kg requires +2-3 hp to maintain speed.
• 🌊 Operating conditions: During the current or headwind, the power is needed 30% more.
• ⚙️ Type of screw: Three blades give the best acceleration, four - economy at cruising speed.

Critical error: set the engine back to power. Caterpillar 3.8m s Mercury 15 hp It will barely crawl against the Volga, although according to the formula "passes". Always take a stock of +20-25%.

3. Gasoline vs diesel vs electric motor: which is best for a catamaran

There's no universal answer, it depends on the budget and the tasks, and let's look at the pros and cons of each type.

⛽ Gasoline engines (2T and 4T)

Two-stroke (2T):

• ✅ Light and compact (art.Mercury 15 It weighs ~36 kg.
• ✅ Cheaper in buying and repairing.
• ❌ Fuel consumption is 30% higher than 4T.
• ❌ Noisy and require mixing oil with gasoline.

Four-stroke (4T):

• ✅ More economical (consumption of 5-7 l / h against 8-10 l / h in 2T).
• ✅ Quiet and green (important for fishing)
• ❌ Expensive and heavier (Yamaha F25 — ~ 70 kg.

⚡ Electric motors

Ideal for quiet fishing or short walks:

• ✅ Silent doesn't scare fish.
• ✅ No emissions, can be used in reserves.
• ❌ Limited power reserve (the battery lasts for 2-4 hours).
• ❌ Dear (set) Minn Kota Terrova 80 + The battery will cost ~200 000 )..

⚠️ Attention: Diesel engines on catamarans are almost not used due to high weight and vibrations, except for large marine catamarans with a length of 7 m, where stationary diesel engines are installed (see below).Yanmar, Volvo Penta).

For most owners of catamarans with a length of 3.5-5 m, the best choice is: four-stroke gasoline engine 15-30 hp It balances price, efficiency and reliability, and electric motors should only be considered for small, homemade designs or as an auxiliary engine.

What engines are banned on catamarans in 2026?

According to the rules of GIMS, on catamarans up to 6 m long, motors with a capacity of more than 60 hp are prohibited without registration of the vessel, and engines with a noise level above 85 dB can not be used (this is almost all 2T engines without a silencer).

Installation of the motor: step-by-step instructions and typical errors

Incorrect installation is responsible for 70% of engine failures on catamarans.

1. Check the transom: It shall be made of aluminum ≥4 mm thick or of laminated plywood (at least 18 mm) reinforced with steel corners.
2. Choose the height of the lower unit:
   • 🔧 Short Shaft (S) 381 mm (for transverses up to 400 mm).
   • 🔧 Long Shaft (L) 508 mm (for trans 400-500 mm).
   • 🔧 Extra Long Shaft (XL) 635 mm (for high catamarans)

Hold the engine: Use it. 4 M10 bolts (not screws!) with growers. Puffing time is 25-30 Nm.

Adjust the angle of inclination (trim): The anticavitation plate should be 0-5 cm above the water level.

⚠️ Attention: If the engine starts up in the nose when it accelerates, then the center of gravity is shifted forward, so the solution is to move the battery or the load closer to the transom.

Typical mistakes of beginners:

• 🚫 Use of the lower unit At a high transom, the screw will "grab" air.
• 🚫 Motor attachment 2 bolts only The vibrations will quickly break the mount.
• 🚫 Ignoring transmunal (It must be 90° to the waterline, otherwise the motor will be taken away.)

5. break-in and the first TO: how to prolong the life of the engine

The first 10 hours of operation are critical to engine life.

The break-in stage	Duration	Max. Turnover.	What do you do?
1st hour	60 minutes.	half-time	Smooth acceleration, no sharp jerks.
2-5 hours	4 hours	half-time	Alternate speeds, avoid long work on singles.
6-10 hours	5 hours	90% of the maximum	You can test the full gas, but not longer than 5 seconds.

After the break-in necessarily:

1. Plug and replace the oil in the gearbox (even if the manufacturer says it is not necessary).
2. Check and, if necessary, tighten the mounting bolts.
3. Examine the screw for damage (small dentures can be removed with a cover).

Critical: If the engine starts to sneeze or stop during break-in, stop immediately and check the fuel system, and a common cause is air entering the hose due to a loose connection.

6. Fuel, oil and winter storage: how to save without harm

The fuel consumption of a catamaran is 15-20% higher than that of a conventional boat of the same length.

• ⛽ Use it. 92nd gasoline (The 95th does not increase power, but it is more expensive.)
• ⛽ Add the type additives. Liqui Moly Speed Tec They clean the carburetor and reduce consumption by 5-7%.
• ⛽ Keep your speed in range 70-80% of the maximum This is the best way to save money.

In oil:

• 🛢 For 2T engines: Motul Outboard Tech 2T or Quicksilver Premium (ratio 1:50).
• 🛢 For 4T engines: Yamalube 4M (10W-30) or Mercury Premium (10W-40).

Winter storage is a separate topic, and if you leave the engine unprepared, you'll be waiting in the spring. jammed Or a corroded gearbox.

1. Pour all the fuel or add a stabilizer (Please).STA-BIL).
2. Replace the oil in the gearbox (even if the engine is new!).
3. Lubricate the cylinders through candle holes (2-3 ml of oil each).
4. Keep the motor in an upright position (screw upwards) to avoid deformation of the glands.

⚠️ Attention: Never store the motor in a plastic case without ventilation, which causes corrosion. cotton-shell.

📊 What fuel do you use for your engine?

92nd gasoline

95th gasoline

Mixture 92+ additives

Diesel

Electricity

7. Tuning and upgrade: when justified

Many catamaran owners want to get more power or efficiency out of the engine, but not all of the improvements are equally useful.

• 🔧 Rotor replacement: For example, from the standard three-blade four-bladed Solas Amita This will give +10% of the thrust at low speeds (relevant for fishing).
• 🔧 Installation of hydraulic lift: Allows you to lift the motor in shallow water, protecting the screw from damage.
• 🔧 Carburetor tuning: Reflashing or replacing chiclers (for example, a set from Mikuni>) can add 5-10% power, but requires customization.

What to do don't:

• 🚫 Install screw-up without checking the gearbox - this leads to its overheating.
• 🚫 Use it. cheap-spin They often have an imbalance that destroys bearings.
• 🚫 Trying. boost up by removing the catalyst - this reduces the resource of the piston group by 2 times.

If you really lack power, it’s better. Sell the old engine and buy a new one. It's a little bit more than you'd spend on a little bit of a little bit of tuning, like the same money you'd spend on a little bit of rework. Mercury 15You can take the b/w. Yamaha 25 in good condition.

8. Frequent breakdowns and how to avoid them

Here are the top 5 problems faced by motor owners on catamarans:

Breakdown	Reason.	How to prevent
Overheating of the engine	A clogged water intake or a faulty pump.	Wash the cooling system after each release into salt water.
High-speed vibration	A bent screw or imbalance.	Check the screw for damage after hitting underwater obstacles.
Bad cold launch.	Contaminated candles or carburetors.	Clean candles every 50 hours and use fuel additives.
Leaking oil from the gearbox	Worn-out gums or damaged seal.	Change the oil in the gearbox every 100 hours or before wintering.
Loss of traction	Screw cavitation or algae-grown gearbox.	Regularly clean the anti-cavitation plate and screw.

If the engine suddenly stalled on water, the first thing to check is:

1. Fuel intake (open the tank cover - if a suction sound is heard, then the hose is clogged).
2. Snap and see if you have any stains or stains.
3. Safety switch (often triggered by a sharp jerk of the line by the handle).

⚠️ Attention: If the engine overheated, You can't just jam it. - Let me work 2-3 minutes on singles to avoid thermal shock.

FAQ: Answers to frequent questions

Can I put a 4.5 m engine 60 hp on a catamaran?

Technically, yes, but It is legally forbidden. without registration of the vessel in GIMS (for engines over 5 hp on boats up to 20 hp and over 60 hp on boats up to 6 m). In addition, such a motor will create an excessive load on the transom and increase the risk of tipping in corners.

Which screw is better for a catamaran: aluminum or stainless?

Stainless (stainless)Stainless Steel) gives +5-10% speed and keeps speed better, but costs 3-4 times more. Aluminum screw is cheaper and "forgives" hits on stones, but wears out faster. For beginners, we recommend aluminum, for high-speed catamarans - stainless steel.

How long does the engine on the catamaran work when properly operated?

The service life depends on the type of motor:

• 🔹 2T engines: 1,500–2,000 hours of motorized oil (with regular oil change)
• 🔹 4T engines: 3,000 to 5,000 hours of motorsport.
• 🔹 Electric motors: Up to 10,000 hours (limits battery life)

With intensive operation (50+ hours per year), even budgetary HDX T15 It'll last 7-10 years.

Do I need to register a catamaran with a 9.9 hp engine?

Not if the length of the vessel is less than 6 m and the power of the engine does not exceed 5 hp (for boats) or 60 hp (for boats). 9.9 HP engine already requires registration If you plan to go out to navigable rivers or the sea, you do not need to register for fishing on a lake or pond.

Can I use car oil for a outboard motor?

Automotive oils are not designed to work in high humidity and do not protect parts from corrosion. For 4T engines, use only specialized oils with labels. FC-W or TC-W3.