FAQ’s Summary

HYDROFIN RangeHydrofoil Body with Down Angle: Improves efficiency and economy by reducing the aeration bubble (known as cavitation) by the propeller drawing down all the water, creating an air bubble.  Manages the water flow as a physical barrier to channel the propeller thrust. Lifts the stern to plane at lower speed / bow down, for improved visibility. Supports the rear of the boat to stabilize side to side rocking motion.  

Dual Rudders : Provide controlled steering by channelling the water flow passing the hull surfaces even at zero propeller revolution. Two rudders with four control surfaces. Course keeping at speeds below 8 knots on those windy days or in a tidal flow.  

Rudder Positioning by Desired Boat Use : Either side of the propeller as follows:

  • Boats used up to 8 knots : Fit rudders down for stability and controlled steering.
  • Boats used over 8 knots :  Fit rudders up for power management, lift and controlled steering.

No Drill, Side Clamping System : Does not over extend rearward into propeller wash. Propeller impact damage, when reversing, reduced, as protected by Hydrofin body and Dual Side Rudders.

Frequently Asked Questions (FAQ’s) : So far !

Can it be fitted with my boat in the water ?
Customers have fitted the hydrofin in 15 minutes rather than the normal 10 minutes with their boat in the water with the leg or outboard in the tilted position, This happens more often than not, due to crane costs mid season. They have been fitted via dinghy, on a slip or in the shallows. The rubber strips can be fitted to the hydrofin body rather than the engine casing when in the water too.

How do I know which size, small or large to buy ?
We state 8hp to 35hp for the small and 35hp and above for the large, same as the USA. However I have fitted the small to a Tohatsu 50hp, so best view the fitting videos and make both templates to test if not sure. Or ask Steve at Safeboat.co.uk for help.

Will I be able to moor up easier ?
Yes, even at zero propeller revolutions and just movement. See the video of Jim mooring his boat on the web site.

How do I know for sure if the slot in the hydrofin body will fit my Outboard ?
The small and large cut outs are on the web site in the Hydrofin Outboard section for you to make a cardboard template that you can take to your boat to offer up.

Why is yours better than my Add a Rudder ?
Your single rudder made of metal is just not good because the metal straps can rub away at your cavitation plate. It is also in the propeller wash and causes vibration and heavy steering, more noticed with cable steering. It also stick out the back a lot. Twin rudders are three times as effective without the issues mentioned.

What do you mean by DIY kit ?
It’s a flat pack full kit. Assembles in 15 minutes with 10mm spanner / ratchet and 10 minutes to fit (15 minutes in water fitting). Some minor finishing may be required, sand an edge, reshape to fit or drill a hole through for clearance. Cut the rubber strips to suit. Nothing too great or to worry about. Full instructions and web site information videos to view.

What tests have you done and what is the warranty ?
Warranty first, 30 day money back with eBay full protection for distance selling, we are a proper shop with good people. Full spares and help back up. Tests: We have sold rudders for many years and twin rudders too. Just designs improve and when we looked at this subject we found design improvements were needed.The hydrofin twin rudder concept has been used in the USA for many years. So has the clamp on system. We have improved these concepts and have a design to out match and go beyond all other products. We have tested the clamp system in the Irish Sea, to over 30 knots with added drag, far beyond those in normal use. The flexibility of rudder positioning, as separate from the main body, is key to allowing this product to suit different boat speed uses. We cater for pottering about and planning speeds and everything in the middle, by design and testing, not by accident.  

What happens if I order a small, change my mind when received, to want a large ?
Just send it back, we get the best pick up prices using Parcel Monkey on line, and you will be refunded as we do not do postal exchanges, just visitors. You can order and pay for the large replacement immediately as they are separate transactions and you get started again quicker. Or come to see us.

Why will the hydrofin help to get on the plane ?
It will get your boat on the plane at a slower speed, thus better economy and efficiency of power use. Lift because of the rear flap design and the body reducing cavitation by aeration draw down.

What is this aeration you mention, I heard it was cavitation ?
Aeration is when the power of the propeller at high speed draws down all the available water to a point where only air is left. This causes air bubbles, reduces thrust and power as no more water. The cavitation plate on you engine is narrow and designed to help with aeration issues hence the “naming” confussion. The clamp on Hydrofin main body increase the width of your cavitation plate and thus improves efficiency in this area.

How do you know the clamp on plate work and it stay on ? I have UK tested the Hydrofin at speeds over 36 knots and also added extra drag to factor in tolerance. The basic clamp system has been tested and used in the USA for five years too.

Are there any fixings to go into my outboard cavitation plate ?
No drilling / No bolts into your outboard or stern drive. This would simply be wrong. Here in the UK we use rubber strips either side of the clamping system to isolate any metal to metal contact to stop vibration damage or galvanic degradation.

Why is your Dual Rudder better than my Rudder Safe Course Keeper ?
Customers who have replaced your unit with the Hydrofin Dual Rudder tell me our unit is much better for steering at slow speeds. I know this is due to the hydrofin main body channeling the propeller force to create the improved steering.

Do I need to fit an anode ?
No anode required as the Hydrofin is one metal type with no cathode/anode galvanic action and the Hydrofin body is isolated by rubber strips when fitted.

How do I set the clamp gap and spacer ?
The spacer is fitted as supplied thickness along with the top and bottom rubber strips as per instructions. You can measure the width of the cavitation plate widest point and set the plates and spacer gap to that measurement, fit with say two hand tight fixings on each plate set, to then slide onto the cavitation plate, to check, before final fitting of all the fixings and the rubber strips.

Why is it made in aluminium ?
Most outboards and stern drives are made of aluminium. Thus, so as not to introduce a “different” metal we use the same. Otherwise there would be potential issues with galvanic action by introducing an anode metal with a cathode metal group. If we produce a stainless hydrofin, this would be okay with our clamp design as we have isolating rubber between the clamping surfaces and no metal to metal contact with the outboard or stern drive unit.

Why do you not paint them ?
We have been asked to by a dealer who wanted a black finish to match their engines. But there are many different colours used by the manufacturers. We drew the line at base metal finish for this reason and one of our customers said “Why do I care, it’s going to get cover in river green and scale in three days !”. Putting on colour would also add a high cost too. Maybe DIY ?.

Why are the small ones rudder downward and the larger one upward ?
This is due to propeller thrust management. The thrust on small outboards low and therefore needs to be channeled below the main plate and between rudder surfaces, so downward. Bigger engines or for higher speed use is different as more forces involved. The extra power is therefore a disadvantage to downward rudders so they are fitted upward. The main force is used for the hydroplane element while the rudders are there for steering at slower speeds when mooring as they are in the water above the Hydrofin main plate.

But the Rudder Safe lifts out of the way ?
Agreed. But only because it has too. Otherwise the steering at higher speed would be heavy for cable steering. Also this product is suspect to damage as it is rearward sticking out, has no hydrofoil and is a mechanical devise and in our hard scale water can be troublesome. Our Hydrofin Dual Rudder has been designed not only to work better but to be more robust.

How does it “Lift, Stabilize and Control” as YOU say ?
The Hydrofoil main body lifts by propeller wash force and this force pressure creates a stabilizing effect to reduce rocking port to starboard by people movement. Control of steering by correctly positioned Dual Rudders.

Why will it stop wandering and my having to correct steering ?
If your boat is wandering the Hydrofin will nearly eliminate this problem by lift, stabilizing and control with the Dual Rudders. Other crew members will be able the take over the steering too and much better.