Question "The S foot on the outboard motor - how much?" It's common for beginners to have to deal with outboard motor markings. "S" in the designation (e.g., Yamaha 9.9 FMHS or Mercury 15 S) Does not indicate the horsepower directlyand lower unit designs This is the so-called "leg" of the motor. the length of the lower unit, the type of gearbox and sometimes the maximum allowable power for a particular model.
To understand how many horses are hidden behind this letter, you need to understand that manufacturers use different designation systemsFor example, the Mercury and Tohatsu letter S mean "short" (short lower unit, 381 mm) and the Yamaha — "standard" (standard, 508 mm). motor capacity is indicated separately in the numbers before the letter index (for example, Mercury 15 S = 15 hp. In this article we will discuss nuances of markingLet's learn. read engine codes correctly And choose the best foot for your boat.
If you have already faced the choice of outboard motor, you know that besides power is important. lower unit length, transmission type (reductor/direct drive) and transcensor compatibilityLetter S And that's what it's all about. Honda BF2.3 S power 2.3 hpBut its leg is short (381 mm), which is suitable for small inflatable boats. Yamaha 30 S - That's it. 30 hp with a standard lower unit (508 mm), which is suitable for aluminum boats with high transomania.
To avoid confusion, remember a simple rule: The letter S is not equal to horsepower. - She's just clarifying. motor-designPower is always indicated. letter-code (for example, Suzuki DF9.9 S = Next, we will discuss in detail how these designations are deciphered by different brands and how to choose a motor that will not damage your boat.
What does the letter S mean in the marking of outboard motors?
Letter S in the name of the motor, it's design, which can mean different things depending on the manufacturer, here are the main decryption options:
- 🔹 Short (short lower unit) - Brands. Mercury, Tohatsu, ParsunThe length of a lower unit is usually 381 mm (15 inches)Suitable for low-transom boats (inflatable PVC, small aluminum).
- 🔹 Standard (standard lower unit) - Yamaha, Honda, SuzukiLength. 508 mm (20 inches)It's a universal option for most boats.
- 🔹 Special (special modification) Less common, but occurs in some models Evinrude or JohnsonIt can denote a unique design of a gearbox or a lower unit.
- 🔹 Single (single cylinder) - Old models Mercury (for example, Mercury 3.5 SHere S indicates the number of cylinders, not the length of the leg.
It is important to understand that The same letter from different brands can mean different things.For example:
- Mercury 9.9 S = 9.9 hp + short lower unit (381 mm).
- Yamaha 15 S = 15 hp + Standard lower unit (508 mm).
To avoid making a mistake, always look. specifications of a specific model if there are other letters in the label (e.g., Yamaha 30 MSHS), then:
- M - manual (manual start),
- S - standard,
- H High Thrust (higher traction)
- S At the end, it can duplicate the designation of lower unit.
How to determine the power of the engine, if the name has the letter S?
Power of the outboard motor always indicated in numbers before the letter indexLetter S (as do other symbols) It does not affect horsepower.It's just a design refinement. Here are some examples.
| Engine marking | Power (hp) | Meaning of the letter S | The length of lower unit |
|---|---|---|---|
| Mercury 5 S | 5 | Short (short) | 381 mm |
| Yamaha 9.9 FMHS | 9.9 | Standard (standard) | 508 mm |
| Tohatsu 18 S | 18 | Short (short) | 381 mm |
| Honda BF2.3 S | 2.3 | Standard (standard) | 508 mm |
| Suzuki DF6 S | 6 | Short (short) | 381 mm |
If in the name of the engine No numbers before the letter S (for example, Mercury Sthat model-notationIn this case, the power can be determined:
- Serial number (usually indicated on the transom plate).
- On the plate with technical data on the engine.
- Through the manufacturer's catalogue by model.
Attention! Some sellers may only list a letter index in ads (e.g., “I’ll sell the S engine”). That's incorrect. Always check the full name of the model and the power.
If you buy a motor with your hands and you only see the letter S without numbers, ask the seller to take a picture of the plate with the serial number, which can accurately determine the model and power through the official website of the brand.
Short (S) vs Standard (S) lower unit: What's the difference?
This is where the confusion begins: some brands S = short (short)Others have S = standard (standard)To be safe, you need to know. lower unit:
- 📏 Short (Short, S) — 381 mm (15 inches)Suitable for transcenuous boats 350–390 mm (inflatable PVC, small aluminum).
- 📏 Standard (Standard, S or L) — 508 mm (20 inches)The universal option for transom 400-500 mm.
- 📏 Extended (Long, X or L) — 635 mm (25 inches)For high transom boats (boats, yachts).
How not to mix it up?
-Of Mercury, Tohatsu, Parsun S = Short.
-Of Yamaha, Honda, Suzuki S = Standard.
-Of Evinrude/Johnson maybe S = Special (Specify in the documentation).
If you choose. too-short-dadewoodThe engine will be “buried” into water, which will lead to:
- increased resistance,
- overheating,
- slowing down.
If it's lower unit too-long..
- the propeller will work in the air,
- the thrust will decrease,
- increases the risk of damage to the screw to the bottom.
What happens if you install a motor with an inappropriate lower unit?
If the lower unit is too short, the motor will be burrowed into the water, causing increased drag and overheating, and if you have too long dayswood, the screw will be too deep, which will reduce efficiency and can cause cavitation, both of which affect the handling and resource of the motor.
Example: If you have a transceived PVC boat 380 mmthe engine Yamaha 9.9 FMHS (S = standard, 508 mmwill too long - We need a model with lower unit (for example, Mercury 9.9 S 381 mm long.
How to find a motor with a "foot S" under your boat?
To choose the right motor with the designation SFollow this algorithm:
- Measure the height of the transanth (water to top edge) Optimal length of lower unit = height of transmunz + 25-50 mm.
- Determine the maximum powerThe boat is in your possession (specified in your passport).
- Check the letter index.:
- If S = Short (381 mm), suitable for transom 350–390 mm.
- If S = Standard (508 mm), suitable for transom 400-500 mm.
- Consider the type of boat.:
- PVC usually requires lower unit.
- For aluminum and hard boats, standard.
Measure the height of the transanx from the water
To specify the maximum power of the boat on the passport
Check the decoding of the letter S for a specific brand
Check the length of the lower unit with the recommendations of the boat manufacturer
Consult with the seller or service center
-->
Examples of selection:
- PVC boat. Flagship 320 (Trans 380 mm, max 10 hp) → Tohatsu 9.8 S (Short, 381 mm).
- Aluminum boat. The winger 360 (Trans 450 mm, max 20 hp) → Yamaha 15 S (Standard, 508 mm).
⚠️ Attention! If the boat data sheet says "maximum engine power of 15 hp" but you set Mercury 20 Sthis breach of GIMS rulesFine up to 2,000 rubles + possible problems with registration.
Common mistakes when choosing a motor with a "foot S"
Many buyers make the same mistakes, which leads to the malfunction or breakdownHere are the most common ones:
- 🚫 Ignoring the height of the transanth - buy a motor with a long lower unit for a PVC boat, because of which the screw works in thehalf-submarine mode.
- 🚫 Confusion in the S decoding - think that Yamaha 9.9 S and Mercury 9.9 S They have the same lower unit (in fact, Yamaha has a longer one).
- 🚫 Exceeding maximum power - put Honda BF20 S on a boat designed for 15 hp, which leads to overloading of the transom.
- 🚫 Buying by eye Do not check compatibility by serial number or catalog.
How do you avoid mistakes?
- Always. check with the documentation on the boat and the motor.
- If you doubt it, Take the motor with adjustable transcension (for example, Mercury with Power Tilt System).
- Before the purchase. check the motor on the water (Many dealers offer a test drive.)
The S on the engine marking is NOT power, it indicates the length of a lower unit or the type of design. Always check the full model name and specifications.
Top 5 engines with "S foot" for different types of boats
We took it. 5 tested models signified SThe best suited for different boats:
| Motor model | Power (hp) | Type of lower unit (S) | Recommended boat | Average price (2026) |
|---|---|---|---|---|
| Mercury 9.9 S | 9.9 | Short (381 mm) | PVC 320–360 cm | ~180 000 ₽ |
| Yamaha 15 FMHS | 15 | Standard (508 mm) | Aluminum 360-420 cm | ~250 000 ₽ |
| Tohatsu 5 S | 5 | Short (381 mm) | PVC up to 320 cm | ~110 000 ₽ |
| Honda BF20 S | 20 | Standard (508 mm) | Aluminum 400+ cm | ~320 000 ₽ |
| Suzuki DF6 S | 6 | Short (381 mm) | PVC 300-340 cm | ~140 000 ₽ |
What to look for when buying?
- Guarantee: at official dealerships Yamaha and Honda before 3-5 years.
- Type of launch: manuallyMor electric ()E).
- Motor weight: for PVC boats optimal 25 kg.
Motors with an S index and power up to 10 hp often do not require registration with GIMS (as of 2026), but always clarify the current rules.
FAQ: Frequent questions about the "foot S" on outboard motors
❓ The Mercury 15 S is 15 hp with a short lower unit?
Yes, in this case:
- 15 - horsepower.
- S - short lower unit (See also:381 mm).
Suitable for PVC transcensor boats 350–390 mm.
❓ Can I put the Yamaha 9.9 FMHS on a 380mm transom boat?
No, that's it. not recommendedUgh. Yamaha 9.9 FMHS lower unit standard (508 mm)It's too long for a transom of 380 mm. lower unit (for example, Tohatsu 9.8 S).
❓ What is the S in the Honda BF2.3 S?
U Honda letter S signifier Standard lower unit (508 mm)The power of the motor. 2.3 hpSuitable for small inflatable boats with transom 400 mm.
❓ Which engine with the S foot is the most economical?
Among the low-power models stand out:
- Tohatsu 5 S (consumer ~2.5 l/h),
- Suzuki DF6 S (consuming ~3 l/h).
Both have short lower unit (381 mm) They're suitable for PVC boats.
❓ Do I need to register a motor with the letter S?
Registration depends Not from the letter S, but from the power.:
- Before. 10 hp registration required (as of 2026).
- Of course. 10.1 hp — mandatory (GIMS license and registration in the register are required).
Example: Mercury 9.9 S (9.9 hp) - not registered, Yamaha 15 S (15 hp) - registering.