WO2006015421A1

WO2006015421A1 - Developments relating to corrosion protection

Info

Publication number: WO2006015421A1
Application number: PCT/AU2005/001183
Authority: WO
Inventors: John Anthony Geeve; Anthony John Whitehall; Paul Joseph Rigg; Desmond John Werner
Original assignee: Vector Marine Pty Ltd
Priority date: 2004-08-11
Filing date: 2005-08-09
Publication date: 2006-02-16

Abstract

An assembly of an outboard motor engine mount affixed to a transom of a boat, said assembly including mounting means for mounting said engine mount on the transom while also electrically insulating the mount from the transom. The mounting means may include a pair of electrically insulating panels affixed to the transom by bolts having surrounding sleeves which carry integrally formed flanges. A detector apparatus is described which tests the integrity of the electrical insulation between an outboard motor and the boat's hull.

Description

DEVELOPMENTS RELATING TO CORROSION PROTECTION

Field of the Invention

This invention concerns the minimization of corrosion in aluminium boats driven by outboard motors.

Background to the Invention

The invention relates to aluminium hulls and outboard motors, which are mounted on aluminium vessels through the transom, and their respective electrical systems.

Galvanic corrosion is a well known condition in aluminium boats with outboard motors. The cause is the electrical connection between two dissimilar metals which are immersed in an electrolyte. The most common place for this corrosion to occur is where the connection of two dissimilar metals are found or placed, for example around the bolts mounting a marine outboard motor to the transom.

Every metal, when immersed in an electrolyte, has its own electrical potential. Similarly, there are no two dissimilar metals that have the same electrical potential. The Galvanic Series Chart, included as Table 1 later in this specification, shows potential electrical voltages of particular metals. The electrical potentials of the metals vary in regards to the conductivity of the electrolyte.

With aluminium boats, the metal that is most vulnerable to corrosion is the aluminium as this is the least noble metal. This risk is increased significantly when the aluminium comes in contact with stainless steel. Dissimilar metals that are in contact with each other and also with an electrolyte will form what is known as a

'galvanic cell'. When a galvanic cell is formed, the metals involved will attempt to equalise their electrical potentials, which over time will corrode the less noble or more active of the metals until the cell is broken, or there is no metal left to consume. This scenario is equivalent to a battery cell that runs out of charge when the less noble material has been destroyed.

Hence on an aluminium boat, the aluminium when connected to stainless steel will begin to break down until the galvanic cell is either no longer present, or the aluminium has been completely corroded.

It is also well known that within aluminium boats, the electrical systems should be fully insulated from the hull. If this is not the case, stray current corrosion will occur. This type of corrosion may create small holes or "pitting" in the hull and thus may significantly shorten the life of the hull.

It is therefore desirable to have a means by which an outboard motor may be electrically disconnected (except than by the water in which it is immersed) from the hull of a boat on which it is mounted. It is also desirable to have a means for monitoring the integrity of such electrical disconnection.

Summary of the Invention

In one aspect the invention provides an assembly of an outboard motor engine mount affixed to the transom of a boat, said assembly including mounting means for mounting said engine mount on the transom while also electrically insulating the mount from the transom. Preferably the mounting means includes:

(i) a pair of panels separated from each other and positioned in the same plane between the mount and the transom, said panels being fabricated of electrically insulating material; (ii) a plurality of sleeves fabricated of electrically insulating material and extending through respective holes in the transom; and (iii) a bolt extending through each sleeve and tensioned by a nut; wherein:

(a) a first end of each sleeve engages within a corresponding hole in said panels; (b) the other end of each sleeve has integrally formed therewith an outwardly extending flange; and

(c) the nut or the head of the bolt is electrically insulated from the transom by the flange.

Preferably the sleeve is compressed along its length by the tensioned bolt so that the sleeve is expanded radially to bear tightly against the walls of the corresponding hole in said transom and the corresponding hole in said panels.

Preferably each panel has a forward side facing the transom and a rear side facing away from the transom, and the forward sides of the panels are adhered to the transom adjacent the edges of the panels.

The forward side may have a groove formed therein adjacent the perimeter of the forward side, said groove containing adhesive by which the panel is adhered to the transom. This also may provide a seal. The forward side of each panel may have an array of ribs and grooves formed thereon. The ribs preferably occupy between 25% and 75%, more preferably between 35% and 65%, of the forward side. The grooves preferably occupy between 70% and 30%, more preferably between 60% and 40%, of the forward side.

In another aspect the present invention provides a detector apparatus to monitor the performance of an electrical insulation between a motor assembly and a hull of a boat, said detector apparatus comprising: - means for measuring the electrical potential difference between said motor assembly and the hull;

- means for indicating by way of a first alarm means when said measured potential difference is within a preset acceptable range; and

- means for indicating by way of a second alarm means when said measured potential difference is above said preset acceptable range. Preferably the first alarm means comprises a first indication light which glows a first warning colour when the measured potential difference is within said preset acceptable range. Preferably the second alarm means comprises a second indication light which glows a second warning colour different to said first colour when said measured potential difference is above said acceptable range. The alarm means may also include an audible sound alarm.

Preferably the detector apparatus also includes means for indicating when the measured potential difference falls within the preset acceptable range. That indicating means may include a light which glows a third colour.

The detector apparatus may include switch means which, when activated, will turn off an audible alarm while leaving an indication light glowing related to the warning.

Brief Description of the Drawings

In order that the invention may be more fully understood there will now be described, by way of example only, preferred embodiments and other elements of the invention with reference to the accompanying drawings where: Figure 1 is a fragmentary elevation view of the rear of a boat modified in accordance with one embodiment of the present invention;

Figure 2 is a view from the rear of the boat shown in Figure 1, but without the engine and engine mount;

Figure 3 is a view of from the rear of some insulating components used on the boat shown in Figure 2;

Figure 4 is a view from the front of the insulating components shown in Figure

3;

Figure 5 is a cross section view through portion of an assembly where an engine mounting bracket for an outboard motor is attached to the transom of the boat shown in Figure 1 ;

Figure 6 is an exploded view of the components in Figure 5; and Figure 7 is a view of a detector/indicator component used in accordance with some embodiments of the invention.

Description of the Preferred Embodiment and Other Examples of the Invention

Referring to the Figures, the boat 10 has an aluminium hull and an outboard motor 4 affixed to the transom 12 by means of an engine mounting bracket 18 which is bolted to the transom. A horizontal shaft 6 allows the motor 4 to pivot vertically relative to the bracket.

A pair of panels 14 is adhesively fastened to the rearward face 13 of the transom 12. The panels 14 are made of electrically insulating material such as polyvinyl chloride (PVC) or other plastics material and are formed in a high pressure moulding machine. The engine mounting bracket 18 is fastened by four steel bolts 20 to the rearward face 13 of the transom 12, each bolt having an engaged nut 21. The panels 14 are sandwiched between the forward side 19 of the bracket 18 and the rearward face 13 of the transom 12.

Each of the bolts 20 pass through a tubular sleeve 22 which itself passes completely through the transom. The sleeve 22 is moulded of electrically insulating material such as PVC or other plastics material and is a sliding fit within its associated hole 15 in the transom. Each bolt 20 is a sliding fit within the bore 30 in its respective sleeve. Each sleeve 22 has an integrally formed flange 24 at one end 25 but has no such flange at the other, free, end 26. A stainless steel washer 23 is fitted beneath the head of each bolt 20 and nut 21.

The insulating componentry thus comprises six pieces: two panels 14, and four sleeves 22. The panels 14 are made of insulating material with a relatively soft shore hardness. The sleeves 22 are fabricated through a high-pressure moulding machine from a slightly harder formulation of insulating material. The insulating components are positioned between the aluminium hull and the mount for the outboard motor. Their primary task is to separate dissimilar metals and create a true above ground electrical circuit between the vessel's hull and the outboard motor.

The sleeves 22 are positioned through corresponding holes 15 in the transom 12. The sleeves 22 are inserted from the forward face 11 of the transom, inserting the free ends 26 through the transom and locating the free ends 26 into corresponding holes 28 in the panels 14. The free end 26 extends fully through the thickness of the panel 14.

The sleeves 22 have a 50mm diameter flange 24 that is 2mm to 4mm thick, which contacts the forward face 11 of the transom 12 and prevents the sleeves 22 from sliding completely through the transom. Each sleeve 22 has an outside diameter of 17.95mm, to provide a sliding fit within an 18mm diameter hole 15 through the transom, and an axially aligned bore 30 which, in use, is filled by the shank of the respective connecting bolt 20.

When installing the insulating components, four holes 15 are drilled through the transom in the appropriate pattern. The four sleeves 22 are fitted into the holes 15 and the free ends 26 fed through the holes 28 in the panels 14. The free ends of the tubes are then trimmed off flush with the rearward side 34 of the panels 14.

Transoms vary in thickness from hull to hull, so the sleeves are supplied (before trimming) at a sufficient total length so they may be cut to custom fit each installation individually. A total sleeve length of about 100mm has been found suitable. Each bolt 20 and nut 21 is then fitted, together with a stainless steel washer 23 under each bolt head and nut, and the bolts tensioned. The panels 14 compress a little around the region of each bolt and this causes the sleeves 22 to be compressed longitudinally so that they swell laterally (radially) to compress tightly against the walls of the holes 15 and 28 through which they are located. The panels 14 and sleeves 22 are dimensioned to accommodate the standard fittings of conventional marine outboard motors. The spacing of the holes 28 in panels 14 conforms with a conventional pattern of holes used for fitting outboard motor mounting brackets to transoms. Two such patterns are in common use, namely a more closely spaced configuration to accommodate motors up to 50hp, and a more widely spaced configuration to accommodate motors of 50hp and above. Thus a different sized pair of panels 14 may be used for larger and smaller motors.

It will be appreciated that the sleeves 22 need to be sufficiently long to pass through both the transom 12 and a panel 14. Transoms vary in thickness between boats, but a total length of 100mm for the sleeve has been found sufficient for general use. As described above, the sleeves are trimmed to length during installation to suit the particular boat.

The two panels 14 used on each transom are not symmetrical and as-viewed in Figure 2 are a mirror image of each other. However identical mouldings are used for each panel because the two panels have respectively opposite faces facing the transom.

The panels 14 have 2mm deep ribs 32 moulded into the forward and reverse sides 33 and 34 respectively. The ribs provide improved rigidity of the panel and also provides a surface which is more resistant to flexing when compressed. Each rib 32 extends in a downwards direction. The rib sections are 5mm wide and 2mm deep, and the overall thickness of the panel 14 is 8mm. Corresponding grooves 31 are created by and between the ribs 32. The surface of the panel is about evenly divided between the portion made up of ribs 32 and the portion made up of grooves 31.

A 2mm deep groove 38 extends around each face 33 and 34 of the panel, 4mm in from the edge 36 of the panel. The depth of the groove 38 is the same as that of the longitudinal grooves 31. A ridge around the perimeter of each face 33 and 34 forms the outer wall of the groove 38 and rises to the same height as the longitudinal ribs

32. The peripheral groove 38 is there to retain a continuous bead of curable sealant which creates a seal around the edges of the panels to prevent water entry between the panel 14 and the transom 12. This removes a source of corrosion problems which may occur if salt-water enters between the panel and transom. The sealant also functions as a bonding agent to adhesively affix the panels to the transom. Most marine grade sealants would be suitable.

On the panels 14, where the free ends 26 of the sleeves 22 insert, the holes 20 are approximately 18mm diameter. There is a 50mm diameter area around these holes 20 that is free of grooves 31 and is the full 8mm panel thickness, to strengthen that area.

With the insulating components in place, the connection of dissimilar metals and the marine outboard motor's electrical systems are insulated between the hull and the marine outboard motor. This substantially reduces galvanic corrosion and also corrosion due to stray currents from the boat's on-board electrical systems. The term stray current corrosion refers to corrosion damage resulting from current flowing through paths other than the intended circuit(s). Stray currents can emanate from a poorly installed electrical circuit or a bad earthing (ground) arrangement.

Although the prime purpose of the panels 14 is to provide electrical insulation, they also provide a cushioning effect between the transom and the motor. While this is an added benefit for aluminium boats fitted with the panels, it may be sufficient benefit in itself to warrant installation on a wooden or fibreglass boat. Installation of the panels 14 and sleeves 22 on a fibreglass transom can also ameliorate the effects of so-called "transom rot' which is due to mechanical failure of the fibreglass reinforced material around the engine mounting bolts through the transom.

There is a need to check whether the hull of a boat is grounded to the on-board electrical systems. One way is to use a 12 or 24-volt test light (dependant on the voltage circuit aboard the vessel). The test light is connected to the positive side of the battery and the test light probe is placed on the hull of the vessel. If the test light illuminates, the electrical circuit aboard the vessel is not above-ground, therefore stray current and galvanic corrosion may be present and continue to pose a risk. It follows that if the test light does not illuminate, the electrical circuit aboard the vessel is above-ground.

If any electrical circuit is grounded to the hull, the following items are at risk:

- Electrical dead short to the vessel's on-board battery(s).

- Battery explosion.

- Hull damage (in the extreme this can result in perforation and sinking). - Damage to on-board electrical equipment.

- Stray current corrosion.

- Enhanced galvanic corrosion.

The present invention may provide an electronic detector apparatus to monitor the performance of the electrically insulating apparatus described above. Whilst the insulating apparatus insulates the hull (aluminium) from the engine gear (stainless steel) in order to prevent the process of galvanic corrosion, the detector constantly ascertains the integrity of the insulation, thus ensuring proper performance. The detector achieves this by monitoring the relative voltage measured at each of the metals, (ie the aluminium and stainless steel) and alerting the user when the metals come into contact.

The detector also detects stray currents that originate from on-board electrical equipment. Stray currents are paths of current that do not flow through the intended path. When the detector detects a fault it activates indicators and alarms to alert the user to the problem at hand. This assists with early awareness of a fault within the electrical circuits aboard the boat, decreasing the potential for hazards and corrosion.

According to the galvanic series chart shown in Table 1, the potential difference between aluminium and stainless steel when immersed in an electrolyte, can reach approximately Iv. Stainless steel being a passive metal measures almost zero volts when immersed in a moderately conductive electrolyte whereas the aluminium being a highly active metal can measure as low as -Iv. However, within certain marine environments, the voltage of the aluminium can vary between -0.3v (when the galvanic cell is formed in a low conductive electrolyte) and -1.4v (when the galvanic cell is formed in a highly conductive electrolyte). The greater the voltage difference between the metals, the greater the corrosive potential. It is generally considered that 0.25v is the minimum voltage difference required between metals to begin significant corrosion.

A preferred form of the detector works by monitoring the voltage difference between relevant aluminium and stainless steel components on the boat. The voltage potential of the two metals will be generated when they are immersed in the same electrolyte. A voltage difference between the metals proves the fact that the components are disconnected, for if the metals were physically connected their electrical potentials would attempt to equalise and therefore measure zero volts.

When the metals are disconnected the voltage difference within certain marine environments can vary between -0.3v and -1.4v. When the metals are connected they will measure zero volts due to the metal's attempt to equalise.

The detector also detects stray voltage when in contact with the hull so as to alert the vessel users and minimise potential hazards aboard the vessel.

Referring to Figure 7, the detector 50 comprises electronic circuitry fitted into a waterproof plastic housing 51 having a volume of approximately 30cm³. The housing has three coloured indicator lights 54, 55 and 56 and a press button switch 58. Alternatively in place of a switch, automated electronic circuitry may operate the detector. The housing 51 is fitted in a suitable highly visible position. Users are alerted to a fault condition aboard the vessel in the manner shown in the following table:

An audible sound alarm (sounder) activates for a set time period when the amber light 55 or red light 56 is activated.

The circuitry in the housing comprises mainly surface mounted components. The core component may comprise a flash-based 8-bit CMOS Programmable Integrated Circuit (PIC) similar to a 12F627A (either an 8-pin or equivalent 14-pin model) microcontroller made by Microchip Technology Inc. This activates the indicators and sounder, which alerts the user to the electrical status of components being monitored on the boat. The circuit is powered using the boat's battery supply, though only operating when the boat's key switch is powering the accessories.

The PIC may utilise two internal comparators as detector circuits. Each comparator circuit has two inputs. One input is connected to the aluminium, and the other is connected to a programmable precision voltage reference, internal to the PIC. The different reference voltages are the trigger levels for each output.

The push-button 58, or in the alternative, the automated electronic circuitry, when activated when the unit is in normal condition (ie green light 54 illuminated) acts as a "LAMP and SOUNDER TEST" by illuminating all indicator lights and activating the sounder. It also acts as an "ACKNOWLEDGE ALARM" input to allow the sounder to be turned off even though the detector is in one of the alarm conditions because the detected voltage is outside the acceptable range (ie amber or red lights illuminated). As an alternative to locating the componentry in a housing dedicated to the detector, the lights and switch may be housed in an instrument which also indicates some other condition or conditions on the boat, such as battery voltage, battery charge rate, engine oil pressure, or the like.

Whilst the above description includes the preferred embodiments of the invention, it is to be understood that many variations, alterations, modifications and/or additions may be introduced into the constructions and arrangements of parts previously described without departing from the essential features or the spirit or ambit of the invention.

For example, the insulating panels may be moulded with the main sides 33 and 34 angled relative to each other to form a taper. This would allow a boat owner to readily alter the motor trim angle.

It will be also understood that where the word "comprise", and variations such as "comprises" and "comprising", are used in this specification, unless the context requires otherwise such use is intended to imply the inclusion of a stated feature or features but is not to be taken as excluding the presence of other feature or features.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that such prior art forms part of the common general knowledge in Australia.

Table 1

GALVANIC SERIES In Flowing Seawater

Alloy/Metal Voltage Range of Alloy vs. Reference Electrode*

Magnesium Anodic or -1.60 to -1.63

Zinc Active End -0.98 to -1.03

Aluminium Alloys -0.70 to -0.90

Cadmium -0.70 to -0.76

Cast Irons -0.60 to -0.72

Steel -0.60 to -0.70

Aluminium Bronze -0.30 to -0.40

Red Brass, Yellow Brass, Naval Brass -0.30 to -0.40

Copper -0.28 to -0.36

Lead-Tin Solder (50/50) -0.26 to -0.35

Admiralty Brass -0.25 to -0.34

Manganese Bronze -0.25 to -0.33

Silicon Bronze -0.24 to -0.27

400 Series Stainless Steels** -0.20 to -0.35

90-10 Copper-Nickel -0.21 to -0.28

Lead -0.19 to -0.25

70-30 Copper-Nickel -0.13 to -0.22

17-4 PH Stainless Steel + -0.10 to -0.20

Silver -0.09 to -0.14

Monel -0.04 to -0.14

300 Series Stainless Steels **+ -0.00 to -0.15

Titanium and Titanium Alloys + +0.06 to -0.05

Inconel 625 + +0.10 to -0.04

Hastelloy C-276 + +0.10 to -0.04

Platinum + Cathodic or +0.25 to +0.18

Graphite Noble End +0.30 to +0.20

These numbers refer to a Saturated Calomel Electrode.

** In low-velocity or poorly aerated water, or inside crevices, these alloys may start to corrode and exhibit potentials near -0.5 V.

+ When covered with slime films of marine bacteria, these alloys may exhibit potentials from +0.3 to +0.4 V.

Claims

1. An assembly of an outboard motor engine mount affixed to a transom of a boat, said assembly including mounting means for mounting said engine mount on the transom while also electrically insulating the mount from the transom.

2. An assembly according to claim 1 wherein said mounting means includes:

(i) a pair of panels separated from each other and positioned in the same plane between the mount and the transom, said panels being fabricated of electrically insulating material; (ii) a plurality of sleeves fabricated of electrically insulating material and extending through respective holes in the transom; and (iii) a bolt extending through each sleeve and tensioned by a nut; and wherein:

(a) a first end of each sleeve engages within a corresponding hole in said panels;

(b) the other end of each sleeve has integrally formed therewith an outwardly extending flange; and (c) the nut or the head of the bolt is electrically insulated from the transom by the flange.

3. An assembly according to claim 2 wherein the sleeve is compressed along its length by the tensioned bolt so that the sleeve is expanded radially to bear tightly against the walls of the corresponding hole in said transom and the corresponding hole in said panels.

4. An assembly according to claim 2 or 3 wherein each panel has a forward side facing the transom and a rear side facing away from the transom, and the forward sides of the panels are adhered to the transom adjacent the edges of the panels.

5. An assembly according to claim 4 wherein the forward side has a groove formed therein adjacent the perimeter of the forward side, said groove containing adhesive by which the panel is adhered to the transom.

6. An assembly according to any one of the claims 4 or 5 wherein the forward side of each panel has an array of ribs and grooves formed thereon.

7. An assembly according to claim 6 wherein said ribs occupy between 25% and 75% of the forward side while said grooves occupy between 70% and 30% of the forward side.

8. An assembly according to claim 7 wherein said ribs occupy between 35% and 65% of the forward side while said grooves occupy between 60% and 40% of the forward side.

9. An assembly according to any one of claims 6 to 8 wherein the forward side of each panel has a flat portion surrounding each said hole.

10. An assembly according to any one of claims 2 to 9 wherein the material of said sleeves is harder than the material of said panels.

11. An assembly according to any one of the previous claims wherein a detector apparatus is provided to monitor the performance of the electrical insulation between the motor assembly and the boat's hull, said detector apparatus comprising: - means for measuring the electrical potential difference between said motor assembly and the hull;

- means for indicating by way of a first alarm means when said measured potential difference is within a preset acceptable range; and means for indicating by way of a second alarm means when said measured potential difference is above said preset acceptable range.

12. An assembly according to claim 11 wherein said first alarm means comprises a first indication light which glows a first warning colour when said measured potential difference is within said preset acceptable range.

13. An assembly according to claim 11 or 12 wherein said second alarm means comprises a second indication light which glows a second warning colour different to said first colour when said measured potential difference is above said acceptable range.

14. An assembly according to claim 12 or 13 wherein said first alarm means includes an audible sound alarm.

15. An assembly according to any one of claims 12 to 14 wherein said second alarm means includes an audible sound alarm.

16. An assembly according to any one of claims 11 to 15 including means for separately indicating when said measured potential difference falls within said preset range.

17. An assembly according to claim 16 wherein said means for indicating when said measured potential difference falls within said acceptable range comprises a light which glows a third colour.

18. An assembly according to claims 14 or 15 wherein said detector apparatus includes switch means which, when activated, will turn off a said audible alarm while leaving a related said first or second indication light glowing.

19. An assembly according to claim 18 wherein if said switch is activated while said measured potential difference falls within said preset range, the lamps of the first and second colours glow and said audible alarm sounds.