Technical Information

Technical Stuff........

More technical stuff?

Tom technical
Fig. 1 – Tom Technical – Original Drawing.

Yes, here you find (some) technical information regarding TOM, like the content of the diesel tank, and how long we can actually run on a full tank. And more important, when we need to refuel. This information is very important for "Routes Planned" and if we have to refuel before we are going on the trip. But there will be way more here.

Also, in this section we will add explanations regarding technical issues and how to take care of those. It might be a lot, but I bet you will find solutions to some of your issues here.

Tom's Actual Measurements

We use TOM's measurements to plan routes.

Measurements What
8,05 meter Length overall
7,3 meter Length over waterline
2,85 meter Width overall
2,40 meter Height (air draft)
1,05 meter Draft
Tom's Measurements Front
Fig.M1 – Tom's Beam, Draft & Height.
Tom's Length
Fig.M2 – Tom's Length.

When you plan routes, you should know the dimensions of your boat. We use the above dimensions and that works fine for us. The 2,40 meter height (air draft) is actually 20 cm higher than the tent is. So that is 20 cm of safety for us.

Abbreviations and more

SOG - STW - GPS - COG

This isn't technical, is it?

Yes it is. Because whenever you are going on a trip that is longer than 30 minutes, you should start planning your trip. And with that, comes calcuating your hull speed, your most efficient speed, fuel usage and more. And to calculate those, you need information and abbriviations. So yeah. If you don't like math, buy a toy boat and play with it in your bath-tub!

What are all those shorthands?

Those shorthands are important to know. They will help you plan your trips properly. The KNRM reports that most vessels running out of fuel miscalculated becuase they only calculated the distance and the time they theoretical needed to travel that distance. Not calculating for current, wind and a generous reserve, might get you into trouble.

Common Abbreviations (Motor Vessels)
Abbrev. Meaning What it tells you (motor use) Measured by Quick example / tip
GPS Global Positioning System Your position, plus movement relative to the Earth (SOG/COG). Essential for reliable nav on rivers/canals/coast. Satellites (receiver) GPS gives ground data. If current changes, your GPS speed/course changes even with constant throttle.
SOG Speed Over Ground Your true speed relative to the Earth (actual progress). Best indicator for ETA and timing bridges/locks. GPS STW 6.0 kt with 2.0 kt against → SOG ≈ 4.0 kt.
COG Course Over Ground The actual direction you move over the Earth. Critical in current: where you’re really going, not where the bow points. GPS (track between fixes) You steer east (090°) but current sets you south → COG might become 110°.
STW Speed Through Water Speed relative to the surrounding water. Useful for fuel/throttle efficiency if you have a reliable log sensor. Log / paddlewheel / ultrasonic speed sensor With current, STW can stay constant while SOG changes—don’t plan arrival times using STW.
ETA Estimated Time of Arrival Predicted arrival time at destination/waypoint. Depends heavily on SOG. Calculated from GPS/route If tide turns, ETA can swing a lot—monitor when approaching bridges/locks.
TTG Time To Go Remaining travel time. Practical for planning fuel checks and crew breaks. Calculated from GPS/route TTG becomes unreliable if you slow down in no-wake zones—expect jumps.
NM Nautical Mile Standard marine distance unit for charts and navigation. Defined unit 1 NM ≈ 1.852 km. Speeds in knots are NM per hour.
kt Knot Standard marine speed unit. Used for SOG/STW and current. Defined unit If you cruise 6–7 kt, a 2 kt adverse current is a big deal for arrival time.

Motor-vessel rule of thumb: for planning time and arrivals, trust SOG/COG (GPS). Current and/or Wind effects show up as differences STW↔SOG.

Calculations and more

Hull Speed - STW - SOG

Why is your Hull Speed important?

Tom's full length
Fig.2 - Tom's full length.

Previous you've learned about SOG and STW. And now you know, what those abbreviations mean, you can actually start using those. Because specifically your SOG will be bound to your fuel usage in combination with distance.
Explanation? Simple: Your engine burns a certain amount of fuel per hour. (We measure in Liters per hour: L/h) So, the time it takes to cross the distance defines your fuel usage. And your boat is using the least amount of fuel when you are having the most efficient speed trough the water. (STW) But to know your most efficient speed, you need to know your (theoretical) hull speed. We assume that you have a water-displacing hull.

How to calculate your Hull Speed

Tom's hull-speed
Fig.3 - Tom's hull speed

Every hull has it's theoretical max speed and so does our Tom. This speed is the speed your hull can have through the water. This is what STW (Speed Through Water) stands for. Calculate your hull speed when you measure in meters: 

Hull Speed (knots) = 2.43 × √(LWL (meters))

Calculate your hull speed when you measure in feet: 

Hull Speed (knots) = 1.34 × √(LWL (feet))

When making (long) trips, we want to know what is the most efficient speed for TOM. Nowadays, the costs of fuel are pretty high, so knowing that most efficient speed (through the water), is only helping to get the longest distances out of a liter. Everybody can just "burn" fuel, but every euro you can save, you can spend on good food, or something nice.

And, when we are going to boat on water with currents, we need to know if the speed trough water is enough to win from the currents. Would be a little stupid when your hull speed is 4 knots, and you have a current against of 5 Knots and you are going backwards, right?

Tom's Hull Speed

Theoretical hull speed calculation in knots and km/hr
Hull Speed Knots KM/Hr
Maximum 6,56 kn 12,15 km/hr
Efficient 5,57 kn 10,32 km/hr

How to calculate the Efficient speed? Take 80% of your theoretical hull speed and you have it!
Or use the calculator below here. (Due to the fact that we, the rest of the world, use the Metric system, put the length of your boat in meters and decimeters: "7,3" or "7.30")

Hull Speed Calculator (Metric)

Enter the length of the waterline (LWL) in meters:

Fuel Information

Details about fuel

Now you know your hull speed, you can calculate your fuel plans

Before you start to run off and plan a trip, you also need to know the size of your fuel tank(s) because those demand when you need to refuel. Calculating how much liters you need, is not enough. You also need to be sure you can "store" that amount. Or that you can refuel before you run out. Open water, like the IJsselmeer, Markermeer, Waddenzee and even the coastal waters of the North Sea demand proper (fuel) planning. For example when you want to visit Helgoland. (Heligoland)

Below is the size of our fuel tank and we are using a very conservative calculation of consumption based upon our previous trips with Tom.

Planning consumption 2.0 L/h · Tank 75L (Ø 35 cm · length ≈ 78 cm)

That is what our "start" point for fuel is. 75 liters and a consumption of 2 liters per hour.

When you need to know more about the fuel-usage, go to our
Here you find planners for refueling and usage.

Note! Always use your own information. The volume(s) of your own fuel-tank(s), the hourly usage of your engine(s).

Fuel System Issues

Due to the fact that there can be so much fuel related issues, we created a separate page for that:

Spare-Parts Information

Details about spare-parts

Taking a trip without spareparts?

That might be pretty stupid! And yes, like already mentioned in one, or even more of the routes, you should bring spare-parts with you. They are mandatory for a nice trip! Because belts might break, and filters might get clogged. Read our information regarding spare-parts and you will be able to fix minor issues yourself.

About spare-parts

Due to the fact that there can be so much spare-parts related things, we created a separate page for that:

Stay tuned for updates on our journey!

Our upgrade plans.