Purchase a selected eligible product and register to get +1 year extended warranty today! Learn more
Dec 26, 2019  •  4 min

How to Find Your Shaft Length

If you are looking for an ePropulsion electric outboard for your boat, choosing the correct shaft length is important. If you go too long it would still work but it may lack performance. You will also risk hitting bottom or submerged objects more frequently such as rocks. If you go too short, that’s the worst scenario as you‘re more than likely going to cavitate.

Please note that ePropulsion has a different shaft length measurement from gas-powered outboards. For electric outboards, the shaft length is measured from the top of the clamp bracket to the center of the propeller. For gas outboards, it’s measured from the top of the clamp bracket to the anti-ventilation plate.

As you can see, our XS is close to S from Mercury. Our S is close to L from Mercury. Our L is longer than L from Mercury. See below.

To find the suitable shaft length, the principle is to make sure the top of the propeller is matched to the lowest point of the transom with at least an extra 10 cm (4’’) space to ensure good water flow underneath the boat.

Hard to put it into practice? Well, in order to get the right outboard shaft length, follow three easy steps blow:

Step 1: Measure the transom height which is the length from the top of the boat transom to the bottom of the boat, as illustrated in the image below:

Step 2: After you get the transom height, add the radius of the propeller (check the user manual, and then technical drawing for the number) to calculate the minimum shaft length needed to make it work.

Step 3: Add another 10 cm (4’’) to the previous calculation for the final ideal shaft length.

Let’s take the Spirit 1.0 Evo Remote, radius of whose propeller is 5.5’’ as shown in the technical drawing, for an example. To match the 1964 16′ Starcraft aluminum boat with 21’’ transom height, the shaft length is supposed to be calculated as the following:


Outboard Shaft Length

So the long shaft outboard motor should be the best choice according to the shaft options available:

Spirit Series Products

Shaft OptionsShaft Length
XS52.5 cm / 20.7 inches
S62.5 cm / 24.6 inches
L75 cm / 29.5 inches

Navy Series Products

Shaft OptionsShaft Length
S63.4 cm / 25 inches
L75.9 cm / 29.9 inches

To make things easy for you, here is a chart to match the ePropulsion outboard shaft length with the transom height directly for your quick reference:

Shaft Length Recommendation

Transom HeightShaft Length
30 cm / 11.8 inches – 40 cm / 15.7 inchesExtra Short*
40 cm / 15.7 inches – 50 cm / 19.7 inchesShort
Higher than 50 cm / 19.7 inchesLong

* Extra short version is available for Spirit series only. The navy series doesn’t have an XS shaft.

* This shaft length chart is for your reference only. The calculation from steps above would be more reliable if you get conflicting results.

This chart gives you a general idea of how to choose the outboard shaft length according to the transom height of your boat. To be more specific:

  • For most small dinghies and aluminum boats under 15ft or 4.5m, extra short shaft or short will work depending on whether the transom height is over 40 cm / 15.7 inches or not.
  • For boats with the transom height higher than 50 cm / 19.7 inches, a long shaft version is more suitable.

There are also extra tips if you are using daysailers, one-design racing sailboats, sport boats, and other sailing boats:

  • For daysailers and short one-design racing sailboats, the ideal outboard shaft length depends on the position of the outboard mount. If you choose Spirit 1.0, we suggest you keep the outboard mount at a lower position to make the XS shaft length work. That’s because XS takes less space to store inside the cabin.
  • For daysailers, sports boats and other sailing boats it’s best to measure the distance from the water line to the top of your outboard mount.

It’s always worth checking with your local dealer on which shaft length they recommend for your boat and local conditions. If you still have any questions regarding the shaft length, don’t hesitate to leave a message to our official Facebook.

You could download the technical drawing of ePropulsion outboard here.

David Wutzler
August 7, 2020

Hi – just to clarify, is the recommendation that the top of the prop is 140mm (5.51 inches) below the bottom of the boat?

Unknown member
August 7, 2020

Hi David, to find the suitable shaft length, the principle is to make sure the top of the propeller is matched to the lowest point of the transom. Thank you.

Dale Gillette
January 28, 2021

This article suggests lining up the top of the propeller to the lowest point of the transom. However, in every photo and video on your website that shows the propeller under water, it appears that the top of the propeller is at least 4-5 inches below the lowest point of the transom. Why?

March 27, 2021

Hi, I would also like clarification please – your manual states the top of the propeller should sit between 100 and 150mm below the lowest point of the hull, but this page suggests 0mm below – could you clarify? For reference, my boat has a 400mm deep transom

Debra Huber
April 21, 2021

Shaft length recommended for a 16 ft Compact Yaught

Jared Jensen
April 28, 2021

This indicates that 0mm is appropriate for faster boats, but for slower boats 2-3″ below the bottom of the boat is better. I doubt it matters a whole lot at the speeds this little motor is going to push a dinghy, and a bigger concern might be keeping the shaft shorter if you beach the dinghy frequently so you can get closer to shore before pulling up the motor.

June 2, 2021

Hello, may I enquire what would be the right size Navy 6.0 for an IRB (Honwave T-40)? Thank you very much.

June 3, 2021

Hi Fab, we’d suggest short shaft Navy for transom height between 400mm – 500mm, and long shaft for transom height higher than 500mm.

June 15, 2021

Considering ordering the Spirit 1.0 Plus. My transom height is 14″ which meets the 15.7″ max transom height criteria of the Xtra Short Shaft. I have heard complaints that the props is too close to the surface of the water. Looking for any feedback or recommendation as to the shaft length? We do go into the shallows from time to time, so I am trying to avoid the extra 4″ of depth with the Short shaft if possible.

June 23, 2021

Hi Rob, we would suggest the Extra Short shaft for your application. Thanks!

July 10, 2021

I have a square stern canoe with a transom height of 17”….will the XS shaft work? Short shaft seem too long.

July 12, 2021

Hi Bill, we would recommend the short shaft for your application. If you are not sure about whether the short or extra short shaft suits you better, you may schedule a test ride with our local dealer by filling up this quick form https://www.epropulsion.com/have-a-dealer-contact-me/

September 9, 2021

I have a Walkerbay 8’ will the extra short shaft work? Not sure of the measurements as the dinks in Florida

September 9, 2021

Hi, I have googled the Waterbay boat and found this measurement. It shows the transom height is around 53cm, which is suitable for the Spirit Long shaft. But it’s better to have your boat measured as well, just in case.

January 15, 2022

Hey, my transom height is 37cm, so i should take the XS shaft according to your shaft length recommendation. But when i calculate tramsom high (37cm) + extra 10cm + prop radius (14cm), the result is 61 cm. That’s very close to the S shaft lenghth of 62cm. So, which shaft should I use?

January 18, 2022

Hello Joris, you can use the XS when your transom is lower than 40cm,thanks!

January 16, 2022

Hi, the transom height of my boat is 38cm. According to your shaft lenght recommendation I should use an extra short shaft. But when i make the calculation transom height (38cm) + extra 10cm + prop radius (14cm), the result is 62cm. Only 0,5 cm less than the short shaft lenght of 62,5 cm. So, should I use the XS or S shaft?

January 18, 2022

Hello Joris, you can use the XS when your transom is lower than 40cm,thanks!

April 7, 2022

I have an Old Town square stern wooden canvas sport boat. The transom height is 16 inches. Which spirit 1.0 ,shaft length would be best?

April 13, 2022

Hello Clay, the L size of spirit 1.0 plus is suitable for you, thanks!

April 15, 2022

What about for a pontoon? Still measure from lowest point of the boat (the actual pontoon)? Or just 4″ below water?

April 26, 2022

Hello Anon, the pontoon is still measure like the usual way that from lowest point of the boat, thanks!

April 21, 2022

I have a wooden tideway dinghy and the total measurement of the transom is 460 mm and the Skeg is 130mm if you take a centre line mounting However if I go 150 mm from the centre line I have a transom size of 410 mm. I am not sure what is the best option standard or long shafts

April 27, 2022

Hello Alastair, based on the situation that you describe, we recommend you to choose the L size, thanks!

April 22, 2022

Hello, I have a 2022 Gala F360 with a 21″ Linear measurement taken tight to the transom in a straight line. The transom angles back about 10ºish. The Gala website calls for a 20″ shaft length gas motor. What would you recommend for Spirit 1.0 shaft length if I will be boating in a mix of shallow and deep water? Thanks!

April 27, 2022

Hello Alex, it mainly depends on your shaft lenth, if it’s shorter than 400mm, then you should choose S size; Otherwise the L size is better, thanks!

Todd Mains
April 23, 2022

I’m planning to buy a RIB 290 CSM/Hypalon and I don’t know the transom height. I’d like to get a Spirit 1.0 plus for it. Which shaft should I get?

April 27, 2022

Hello Todd, you can measure the shaft length of your boat. If it’s under 400mm, then you can choose S size; Otherwise the L size is better, thanks!

Jim M
May 1, 2022

I have a new Sea Eagle PaddleSki 437 pontoon type boat. It is in my garage, from the top of the transom to the concrete floor is approx. 20 inches, with my weight in the back it may sink lower into the water. What shaft do you recommend S Shaft or L Shaft?

May 12, 2022

Hello Jim, based on your situation we recommend you the L size, thanks!

April 13, 2023

Hey Jim, we have the same boat. What did you end up with? Does the PaddleSki 437 transom actually sit 20 above the water or more like 17” once it’s loaded on the water?

Jeff Norment
May 8, 2022

For proper mounting height the Spirit 1.0 instruction manual Does Not add 4″ to the transom height (top of transom to bottom of boat), so the top of the propeller is 4″ below the boat bottom. Why does the manual advise the minimum length rather than the ideal length?

May 12, 2022

Hello Jeff, the mounting height of the outboard affects the running speed seriously.When the mounting height is too high, ventilation may occur to waste power.When the mounting height is too low, the water resistance will increase and it will lead to efficiency and running speed reducing.Thanks!

August 16, 2022

Will there be a US version of an anti-cavitation plate for the Spirit? I see only one for the Navy, and it looks like the Spirit version is currently only available in Australia from ePropulsion as S1-AP00-00
ePropulsion SPIRIT 1.0 Anti-Cavitation / Anti-Ventilation Plate.

August 18, 2022

Hi Solar, you can contact our sales manager Alvin(alvin@epropulsion.com) for further informations about the anti-cavitation plate for spirit series, thanks!

John Branner
July 25, 2022

I have a wooden 14′ row boat ( cosine wherry). Transom measures 18″ and has a skeg of 6″
I plan to use in shallow water. Please advise on shaft length

August 9, 2022

Hi John, we recommend you the L size, you can contact the local dealer for further informations: https://www.epropulsion.com/find-a-dealer/, thanks!

Ramez Haddadin
August 7, 2022

I have a Gemini 3400 sailing catamaran. We are interesting in mounting the ePropulsion Evo 6.0 on the central transom. This transom would require a mounting brack. We have 17″ if vertical space on the transom to mount a jack for the motor. The bottom of the central transom is 15″ above the water level. Do you think the long shaft would work well? Would the propeller be submerged? Do you have a mounting jack you would recommend?

August 15, 2022

Hi Ramez, if the transom height is between 400-500mm we recommend you the S size, if it’s over 500mm then the L size is more suitable, you can contact the local dealer for further informations: https://www.epropulsion.com/find-a-dealer/, thanks!

Join the discussion!

ePropulsion and Cookies

This site uses cookies to personalize your experience and analyze site traffic. By clicking accept or continuing browsing the site, you are agreeing to our use of cookies. See our Privacy Policy here.