Welcome to the Hull Coating Calculators
This guide will help you choose the right tool for your question. The calculators are split into two groups: assessing the cost and planning the job.
Tip: Click on any product name (e.g., SML Ballastic Black 📄) in the tables to open its official Technical Data Sheet in a new tab. This is useful for verifying the data used in these calculations.
Cost Comparisons
- Cost per Solid Volume: Use this to find the true value of a paint. It shows how much protection you get for your money, ignoring the solvent that evaporates.
- Cost per Area: Use this for budgeting. It calculates the actual amount you will spend at the shop to buy enough paint for your specific boat.
- Coat-for-Coat: Use this to compare the result of your labour. It shows how much protection you get for applying the same number of coats with different products.
- Manufacturer's Spec: Use this to see the official plan. It calculates the cost and number of coats needed to do the job to the manufacturer's standard.
- 10-Year Ownership: Use this for long-term planning. It compares the total cost of different paint systems over a decade, including repainting and dry-dock fees.
Application Planning
- Drying Times: Use this to see how long you need to wait between coats at different temperatures.
- Total Time: Use this to estimate the total project duration, from the first coat to the final cure.
- Weather Window: Use this to make a Go / No-Go decision on the day of painting, helping to avoid coating failure due to bad weather.
Narrowboat Hull Coating Calculators
Tools to help you compare and select the best coating for your steel hull.
1. Your Hull Dimensions
Total area to be painted: m².
2. Cost Comparisons
3. Application Planning
Cost per Solid Volume (£/Litre of Solids)
This reveals the true cost of the paint based on the volume of protective solids left after the solvents evaporate. A lower cost per solid litre offers better value and often relates to needing fewer coats.
| Product | Price (5L) | Volume Solids (%) | Cost per Solid Litre |
|---|---|---|---|
| 📄 |
How is 'Cost per Solid Litre' Calculated and Why is it Meaningful?
This metric reveals the true value of a paint beyond the price on the tin. When you buy paint, you are paying for two components: the solids (the protective material that stays on the hull) and the solvents (the liquid carrier that evaporates into the air).
The calculation is a two-step process:
- First, it finds the price per litre of the liquid paint (e.g., a £36.00 tin divided by 5 litres = £7.20 per litre).
- Then, it divides this price by the 'Volume Solids %' to find the cost of one full litre of just the solid, protective material.
This allows for a true "apples-to-apples" comparison of what you are actually getting for your money. A cheap paint can be a false economy if it is mostly solvent. A lower 'Cost per Solid Litre' indicates better value, as you are paying less for the material that actually does the job of protecting your hull.
Drying & Overcoating Time Planner
Compare the time required between coats and for the final cure. This is essential for planning your blacking job, especially in variable weather conditions.
| Product | Touch Dry (hrs) | Hard Dry (hrs) | Min. Overcoat (hrs) |
|---|---|---|---|
| 📄 |
*Drying times are calculated estimates based on data sheet values. Products without detailed temperature data will show 'Data only for X°C' unless the selected temperature matches.
Total Application Time Calculator
Estimate the total project time from the first coat to the final hard dry, based on the number of coats you plan to apply.
| Product | Total Project Time (Hours) | Total Project Time (Days) |
|---|---|---|
| 📄 |
How is 'Total Est. Time' Calculated?
This figure represents the entire project duration, from applying the first coat until the final coat is fully cured and hard dry. It is not just the time spent painting.
The formula used is:
(Number of Coats - 1) x Overcoat Time + Final Hard Dry Time
Some products have a very long 'Hard Dry' time specified by the manufacturer, which can make the total project time seem long. This final curing period is often the largest part of the total duration. For a consistent comparison, all 'Total Est. Time' calculations are based on the product's drying data at 23°C. If a product's data sheet does not provide enough information to calculate the time at this temperature, it will be marked as 'N/A'.
Cost per Area Calculator
Calculate the material cost to cover your hull for a specific number of coats. This helps in budgeting for the job based on actual coverage rates.
| Product | Coverage (m²/L) | Litres Needed | Total Cost |
|---|---|---|---|
| 📄 |
Is it in the datasheets? Yes, this figure is always found in the official technical data sheet for the paint. It is the manufacturer's stated coverage.
Is it a wet or dry micron count? The calculation is based on the final Dry Film Thickness (DFT). This is the thickness of the actual protective coating left on the hull after all the solvents have evaporated. This is why the volume solids percentage is so important in the formula.
Why might the calculator's coverage differ from the datasheet?
You may notice the calculator's coverage figure is different from the headline figure on the datasheet. This is because:
- Datasheets often quote a theoretical coverage based on a very specific Dry Film Thickness (DFT), which might be for an industrial spray application (e.g., 500 microns).
- This calculator may use a more practical DFT that is realistic for a brush or roller application (e.g., 250 microns).
Remember, if you apply the paint half as thick, you will cover twice the area. The values used here aim to give a more realistic estimate for your project.
Coat-for-Coat Comparison
Unsure of how many coats?
Simply enter how many coats you intend to apply. The table will show you the total thickness (protection) you will get from each product for the same amount of labour. This allows a true "apples-to-apples" comparison of value. A high-build paint might give you twice the protection of a cheaper one for the exact same number of coats.
| Product | DFT per Coat (microns) | Total Protection (microns) | Total Est. Cost | Total Est. Time |
|---|---|---|---|---|
| 📄 |
*Total Cost & Time require Hull Dimensions to be entered above. DFT per coat is based on typical brush/roller application from data sheets or realistic estimates where not specified.
Why does the 'Total Protection' differ for each product?
This is the key insight of this calculator: one coat is not equal across different products. The total protection differs because each paint is formulated to leave a different Dry Film Thickness (DFT) after a single coat dries.
- A high-build epoxy might be designed to leave a thick 250-micron layer.
- A conventional bitumen paint might only leave a 40-micron layer.
This calculator multiplies the number of coats you enter by each product's unique "DFT per Coat" value. It allows you to compare the true protective result you get for the same amount of labour.
How is 'Total Est. Time' Calculated?
This figure represents the entire project duration, from applying the first coat until the final coat is fully cured and hard dry. It is not just the time spent painting.
The formula used is:
(Number of Coats - 1) x Overcoat Time + Final Hard Dry Time
Some products have a very long 'Hard Dry' time specified by the manufacturer, which can make the total project time seem long. This final curing period is often the largest part of the total duration. For a consistent comparison, all 'Total Est. Time' calculations are based on the product's drying data at 23°C. If a product's data sheet does not provide enough information to calculate the time at this temperature, it will be marked as 'N/A'.
Manufacturer's Specification
This calculator provides the "official" plan. It shows what is required to meet the manufacturer's recommended thickness for proper, long-term protection. It translates their technical data sheet into a practical work plan, showing the true cost and time to do the job to their standard.
| Product | Target DFT (microns) | Coats to Meet Spec | Total Est. Cost | Total Est. Time |
|---|---|---|---|---|
| 📄 |
*Target DFT is based on manufacturer recommendations or industry best practice where not explicitly stated. Total Cost & Time require Hull Dimensions to be entered above.
How is the 'Total Est. Cost' Calculated?
The 'Total Est. Cost' is the price of buying enough paint to meet the manufacturer's official standard for your specific boat. The calculation is a three-step process:
First, it determines the 'Coats to Meet Spec'. It takes the "Target DFT (microns)"—the total thickness the manufacturer recommends for proper protection—and divides it by that product's unique "DFT per Coat" value, rounding up to the next whole number.
Next, it calculates the total paint volume needed. To do this, it uses the hull dimensions you entered in the 'Your Hull Dimensions' section above. It calculates the total litres required to apply the necessary number of coats to that specific area.
Finally, since paint is usually sold in 5-litre tins, the calculator determines how many tins you must purchase to get that volume (again, rounding up, as you cannot buy partial tins) and multiplies that number by the price per tin to get the final cost.
For this calculation to be accurate, it is essential that your hull dimensions are entered correctly above.
10-Year Ownership Simulator
The price of paint is only one part of the total cost of hull maintenance. This simulator projects the true cost over a decade by including repeat applications, preparation, and dry-docking fees. It allows you to accurately compare the long-term financial implications of sticking with a bitumen system versus making the significant one-time investment to upgrade to epoxy.
Define Your Costs
Select Products to Compare
Compare 10-Year Scenarios
Bitumen System Scenario
Projected 10-Year Total Cost
Epoxy System Scenario
Projected 10-Year Total Cost
Please Note: This projection is based on the material and service costs you have entered today. It does not account for future inflation or potential price increases over the 10-year period.
*Material costs are based on the hull dimensions entered above and coats needed from the 'Manufacturer's Specification' tab. The Epoxy scenario assumes a one-time grit blast cost for the first application, with standard prep for any subsequent applications.
Weather Window Advisor
Applying paint in the wrong conditions is a primary cause of coating failure. This tool helps you make a "Go / No-Go" decision based on real-time weather data. For most paints, the steel temperature must be at least 3°C above the dew point to prevent a microscopic, invisible layer of condensation from forming on the hull. Even if the steel feels dry to the touch, this moisture will ruin the paint's adhesion and lead to premature failure.
This is a risk even on the vertical sides of the hull. Because steel is an excellent thermal conductor, the large mass of the boat (especially the base plate) holds the cold from the previous night. This cooling effect is conducted up the sides, meaning the steel can be significantly colder than the surrounding air, creating the perfect conditions for dew to form.
Calculated Dew Point: . Required minimum steel temperature (Dew Point + 3°C): .
| Product | Min Temp (°C) | Recommendation | Reason |
|---|---|---|---|
| 📄 |
How to Find Your Weather Data
To get an accurate recommendation, you need three pieces of information for the day and time you plan to paint:
- Click the button below to open the Met Office weather forecast in a new tab.
- Enter your location to find the local forecast.
- Find the **"Temperature"** and **"Humidity (%)"** values for the hour you intend to paint. Enter them into the calculator.
- For **"Steel Temperature"**, you must use a surface thermometer on the hull itself. The steel temperature can be very different from the air temperature, especially if the boat is in direct sun or has been in cold water. This is the most important measurement for an accurate dew point calculation.