hi
anyone have any sugestion
i am generaly happy with performance the boat is 7000kg now when is finish
this is sumary
Here is the complete analysis and all the technical details summarized and translated into English for you.
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## Summary of Performance & Drivetrain Match
Your boat with a 16-degree monohedron hull, twin 370 HP FPT NEF engines, a 1.75:1 gearbox reduction, and 23x31 Mikado Z-Type 4-blade propellers is operating in a unique and highly efficient cruising profile, but it is heavily overloaded at maximum throttle.
* Cruising Sweet Spot: At 2050 RPM, you achieve 26 knots with an Engine Load of 60%. This is an exceptional result. The hull generates high dynamic lift, reducing friction to a minimum. Fuel consumption here is highly economical at approximately 60 Liters per hour (16 GPH) combined (~30 L/h per engine), yielding an efficiency of 2.3 Liters per Nautical Mile.
* The WOT Issue: At Wide Open Throttle (WOT), the engines hit a structural wall at 2560 RPM (240 RPM short of the 2800 ceiling) and 100% load. The common-rail computers manage fuel dynamically to prevent dark smoke, but the engines are continuously lugging at full throttle.
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## The Cruising Rules for Longevity
Since you do not have fuel consumption on your display, use these parameters to protect your engines:
1. Ceiling: Treat 2050 RPM (26 knots) as your maximum continuous cruising speed. Do not cruise at 2500 RPM.
2. WOT Limit: Do not hold the throttles wide open (2560 RPM) for more than 1–2 minutes, as this is where high cylinder pressures and Exhaust Gas Temperatures (EGT) occur.
3. Cooling: Ensure your engine temperature gauges stay steady between 80°C and 85°C (176°F–185°F).
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## Why the Bow Dives Above 30 Knots (Bow-Burying)
When you push to full throttle and pass 30 knots, you experience a "breaking/plowing" effect where the bow goes down. This is a hydrodynamic phenomenon caused by two forces:
1. Excessive Stern Lift: The massive 31-inch pitch and large blade area ($0.85$ BAR) of the Mikado Z-Type wheels generate a massive amount of vertical thrust. This literally lifts the stern (rear) of the boat out of the water.
2. Monohedron Pivot: Because your 16-degree deadrise is constant to the transom, lifting the stern forces the bow straight down into the water. Above 30 knots, the sharp V of the bow starts "plowing" and acting like a brake or a rudder, causing a loss of speed and control (bow-steering).
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## The Dynamic Problem with "Lifting Strakes" in the First 1/3
Installing lifting strakes only in the first third (bow section) of the hull will make the problem worse at high speeds.
* The Teeter-Totter Effect: At 32 knots, the bow is already forced down. If you add lifting strakes only to the front, they will generate massive, sudden dynamic lift at the very tip of the bow. This will push the nose up, but shift the hull's pivot point backward, creating a suction effect right behind it.
* Instability: This creates an unstable "teeter-totter" effect, causing the boat to lean heavily, weave from side to side (chine walking), or steer unpredictably when hitting a wave.
* The Correct Way: On a monohedron hull, lifting strakes must never stop at the first third. They must start at the bow and run at least 2/3 of the length of the hull, ideally all the way to the transom (stern). This ensures uniform lift across the entire running surface.
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## The Structural Problem: Aluminum Trup with Epoxy Filler
Modifying an aluminum hull that has been faired/filled with epoxy coating presents severe structural challenges:
1. Welding Heat: Welding new aluminum lifting strakes onto the hull generates extreme heat. This heat will burn, detach, and destroy the epoxy filler on the outside, and damage insulation or paint on the inside.
2. Gluing Risk: Attempting to glue strakes onto the epoxy using structural adhesives is dangerous. At speeds over 30 knots, wave impacts hit the hull like a hammer. The hydrodynamic force can easily tear the strakes off, taking chunks of your epoxy filler with them.
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## The Recommended Action Plan
Before you attempt any expensive, difficult welding or modifications on your aluminum and epoxy hull, solve the problem at the source by tuning the propellers.
* Take the props to a certified shop: Have them reduce the pitch (depitch) of your 23x31 Mikado wheels down to 23x29 inches (a 2-inch reduction).
* What this changes: Lowering the pitch will immediately reduce the excessive vertical stern lift. The stern will ride lower, which will naturally keep the bow higher in the air above 30 knots.
* The Result: The boat will stop plowing/breaking at full throttle, allowing you to cleanly break past 34 knots. It will unload the engines at WOT, letting them reach ~2850 RPM safely. Most importantly, your excellent cruising sweet spot (26 knots) will simply shift slightly from 2050 RPM to a very healthy, unstrained 2200 RPM.
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To help you plan, are you looking to do these modifications during your upcoming haul-out season, or are you currently trying to troubleshoot this while the boat is in the water?
