Diesel Pro Power, Inc. keeps  marine engines running in the tourism trade.

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Disclaimer

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Diesel Pro Power is not a tax expert or accountant. This guide is for general information only. Always talk with a licensed tax professional before making decisions about your business or taxes.

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Why This Guide Matters

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If you work in marine tourism—like fishing trips, dive charters, or yacht rentals—2025 brings a big opportunity. A new tax law called the One Big Beautiful Bill (OBBBA) allows business owners to take the full boat cost off their taxes right away. That can help save a lot of money.

If your American boat uses Detroit Diesel, Cummins, or Caterpillar engines, this guide is key for you. It explains what the rule does, how to use it for boat plus engine costs, and how to follow the rules in easy words. (Click Here To See A More In Depth Guide On Tax Write Offs For A Tourism Boat In 2025)

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What Is Bonus Depreciation?

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“Bonus depreciation” means you can write off the entire boat cost in one year when certain conditions are met.

Thanks to OBBBA, if you buy and begin using your boat for business after January 20, 2025, you can use 100 percent bonus depreciation. That means your business could deduct the boat’s cost all at once, not over several years.

This can help you move your business faster and grow more quickly.

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What Counts as Business Use?

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To use this tax break, your boat must be used for business more than 50 percent of the time.

Business means:

• Paid fishing trips

• Paid dive or snorkeling tours

• Paid sightseeing or yacht charters

• Rentals to other paying tourists

Personal use—like family fun days—should be kept below 50 percent. If it’s more than that, you will need to figure out which portion is business use and write off only that part.

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Who Gets the Tax Break?

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If you own a tourism boat business, who gets the deduction depends on your business type:

• You alone (also called a sole proprietor): You enter the write-off on your personal tax form.

• You and a partner: Each one claims part of the write-off based on ownership.

• You run a company (S or C corporation): The company takes the write-off.

If you just invest but don’t work in the business, you may have limits on how much you can deduct.

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Real-Life Examples

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Here are three easy stories to show how it works:

Example 1: Captain Joe’s Fishing Boat

• Buys a clean, strong fishing charter boat for $260,000 in March 2025.

• Runs it every day for paying guests.

• Deducts the full cost in the first year.

Example 2: Dive Tour with Two Owners

• Partners buy a dive charter vessel for $400,000.

• They share ownership. One dives; one handles bookings.

• They divide the tax write-off accordingly.

Example 3: Yacht that Is Part Charter, Part Personal

• Owns a yacht and rents it out 60 percent of the time.

• Keeps it for family 40 percent of the time.

• Deducts just the 60 percent of cost that is business use.

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Engine Parts and Tax Deductions for Marine Tourism Operators

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Using Detroit Diesel, Cummins, or Caterpillar Engines

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When you run a charter boat or other marine tourism business, you depend on your engine every day. Whether you’re offering fishing trips, dive tours, or yacht cruises, your engine must work safely and smoothly.

That means you will often need to buy engine parts—either for regular maintenance or for unexpected repairs. The good news is: these parts can be written off on your taxes if your boat is used for business.

This section explains how that works and gives real examples for Detroit Diesel, Cummins, and Caterpillar marine engines.

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What Counts as a Tax Deduction?

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A tax deduction is something your business can subtract from its income when you file taxes. This lowers the amount of income you have to pay tax on.

If you use your boat to make money—like by taking tourists on fishing trips—you can deduct the cost of engine parts, just like you can deduct fuel, insurance, and marketing costs.

Important: The IRS requires that the parts be for a boat that is used at least 50% for business. If you only use your boat for fun, you can’t deduct engine parts.

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Examples of Engine Parts You Can Deduct

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Here are parts that often qualify as tax deductions for marine tourism businesses:

• Raw water pumps

• Oil filters

• Fuel filters

• Turbochargers

• Impellers

• Gasket sets

• Injectors

• Cylinder heads

• Pistons

• Cooling system parts (like thermostats and heat exchangers)

• Valve kits and rebuild kits

If the part is used to maintain or fix your engine, and the boat is used for a money-making business, it is usually deductible.

Let’s break this down by engine brand. The prices below are just examples to show you how it works, they are not real prices.

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Detroit Diesel Engine Parts: What You Can Deduct

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Many charter boats still run on Detroit Diesel engines, like the 6-71, 8V71, 12V71, or 8V92 models. These engines are known for their strength and long life.

If you use a Detroit Diesel engine in your business, you may need to replace parts such as:

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Example 1: Impeller for Raw Water Pump – Detroit Diesel 6-71

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Let’s say you take out dive groups five days a week. Your 6-71 engine has a raw water pump that’s starting to wear out. You order a new impeller from Diesel Pro Power and replace it during routine maintenance.

• You paid $85 for the impeller

• You paid a mechanic $120 to install it

Total deductible cost: $205
Because the boat is used 100% for business, you can deduct the entire amount.

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Example 2: Blower Repair – Detroit Diesel 8V92

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If your charter yacht uses a Detroit 8V92 and the blower (a key air intake part) needs rebuilding, you might buy a blower gasket set and send in the core for a rebuilt unit.

• Blower gasket set: $250

• Rebuilt blower: $1,500

• Labor: $400

Total deductible cost: $2,150

These are all valid tax deductions if the vessel is part of your charter business.

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Cummins Marine Engine Parts: What You Can Deduct

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Cummins engines are popular in fishing and tour boats. Common models include the 4BTA, 6BTA, QSB, QSC, ISC, and N14.

Cummins engines are known for their simplicity and reliability. But they still need care.

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Example 3: Turbocharger – Cummins 6BTA

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Your diesel tour boat has a Cummins 6BTA engine. The turbocharger stops spinning correctly, and you notice reduced power and black smoke. You buy a new turbocharger.

• Turbo unit: $1,300

• Installation labor: $350

Total deductible cost: $1,650

That’s a big cost—but 100% deductible if your boat is used for tours and charters.

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Example 4: Cooling System Maintenance – Cummins QSB 6.7

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If you’re running longer routes in warm waters, your raw water pump and heat exchanger may need service. You order a pump rebuild kit and a new thermostat.

• Pump kit: $200

• Thermostat: $40

• Shop labor: $160

Total deductible cost: $400

Again, all of these costs go on your tax return as business expenses.

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Caterpillar Marine Engine Parts: What You Can Deduct

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Caterpillar makes heavy-duty engines like the 3208, 3406, 3408, and 3412, which are often found in bigger sportfishers and dive boats.

These engines can go thousands of hours, but maintenance is essential.

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Example 5: Injector Set – Caterpillar 3208

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Let’s say your Cat 3208-powered vessel starts running rough and smoking. Your mechanic finds two faulty injectors and recommends replacing all eight for balance.

• 8 new injectors: $2,000

• Labor: $600

Total deductible cost: $2,600

These injectors directly support business operations—therefore, deductible.

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Example 6: Cylinder Head Gasket – Caterpillar 3406B

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A blown cylinder head gasket could keep your boat out of service. You act fast and buy:

• Head gasket set: $450

• Head bolts: $75

• Labor: $900

Total deductible cost: $1,425

If you keep receipts and log the repair, it’s tax-deductible.

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What About Rebuild Kits?

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Sometimes you don’t replace just one part—you may overhaul the whole engine.

A rebuild kit (pistons, liners, rings, gaskets, etc.) can cost several thousand dollars. That full amount may be deducted in the year you pay for it, as long as it supports a charter or tour operation.

For example:

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• Full rebuild kit for a Cummins N14: $3,800

• Machine shop labor: $1,200

• Mechanic install: $2,000

Total deductible cost: $7,000

That’s a major repair—but fully deductible if your engine is powering a tour boat.

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Key Tips to Make It Work

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• Track business use: Write down every trip and log income.

• Keep every receipt: Save invoices from Diesel Pro Power and other vendors.

• Log the engine hours: Especially if you use your boat part-time for personal use.

• Talk to a CPA: A tax pro can help you claim everything correctly.

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Keep Records to Stay Safe

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To follow the rules, keep these items:

• Boats purchase and usage log

• Engine part receipts

• Trip log with passenger and date details

• Proof of business and personal use split

• Repair and maintenance log

In better words, write it down so you can show it later if needed.

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Selling the Boat Later

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If you sell your boat later and get money for it, part of that can be taxed again based on the earlier write-off. This is called depreciation recapture. Even so, the original tax benefit can help your business grow in the early years.

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Tips to Do It Right

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• Use the boat for business at least 50 percent.

• Buy after January 20, 2025 to get the bonus depreciation.

• Keep your records organized—receipts, logs, calendars.

• Consult a tax professional who knows about charter and tourism boats.

• Buy good parts! Engines run longer with reliable gear—

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Want to Learn More?

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We also wrote a more detailed guide (with tax examples and expert advice) for charter operators. You can read it here: [Insert link to your full article]

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Why Diesel Pro Power?

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At Diesel Pro Power, we help marine tourism workers like you keep your boats running strong. We offer:

• Parts for Detroit Diesel, Cummins, Caterpillar marine engines

• Fast shipping, global support, expert advice

When your boat is ready and engine works great—that’s when you can focus on tours and tours.

Visit dieselpro.com to explore parts. If you have questions about charter operations, we’re here to help.

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In Summary (Plain Table)

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Final Note

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This guide helps explain how the new tax rule in 2025 can boost your marine tourism business. We’re not accountants, but we know engines and boats. Visit our store for parts. For tax help, talk to a real tax advisor.