Thinking out of the proverbial box for a minute, where is your steering cable relative to the aux clamps when installed? (could measure clamp height on the Port side & compare with the toob) . I know this will be a right royal PITA, but if it is above the clamp screws when the aux is installed, I bet you could remove the steering toob, fit the aux, then reinstall the steering over the top of the aux clamps. Worst case loosen the engine bolts to get the Aux clamp past, and reinstall. The steering toob over the top of the clamp would also make it more difficult to nick!
Or for the maximum hassle, if we are on the subject of unbolting the main, all the talk of raising engines by a hole for better performance etc, could you "jack" the main up a hole so the steering bowden clears it completely?
I got lost in all the posts a long time ago but I have a new 2011 3.5hp Tohatsu which has only used 1 tank of petrol - didn't need it in the end It also has an extension throttle/steering arm so you can control the steering and throttle when you are further up the boat .
Details are in the for sale section somewhere but perhaps I ought to keep it as an auxiliary for my proposed RIB but I shouldn't really need one for local trips and modern engines are very reliable!! - shame to sell it though lovely engine........
Just an observation re the steer with the main engine and use the aux to just push you concept.
I had an engine stop on a twin rig rib and the drag of the one stopped one in the water was stunning. Even with another 200+hp of good engine I could only get to 14knts ish with the stopped engine in the water.
Once lifted it was like taking the brakes off and we popped up to 20+ easily.... now consider this as I had a worlds biggest aux engine ( ok maybe not propped right ) ....
If I'd 'only' had 5-10hp ( allowing for the prop set up etc) the main engine still being pulled through the water with the prop spinning freely would make a BIG differance to how quickly I could get places ( or away from nasty places).
understood pete, but 5hp not gonna get you planing anyway, faster the speed the more effect the dragging leg will make, at displacement speeds i dont think the difference would be that dramatic?
understood pete, but 5hp not gonna get you planing anyway, faster the speed the more effect the dragging leg will make, at displacement speeds i dont think the difference would be that dramatic?
defo agree. I guess just more an question of trying it to see if people are happy with it and know what will happen when a main engine stops and the aux is made to earn its place.
Maybe we need a 'RIBNET try my aux engine day' so people can offer things up, without having to buy then can see what works/fits etc ?
understood pete, but 5hp not gonna get you planing anyway, faster the speed the more effect the dragging leg will make, at displacement speeds i dont think the difference would be that dramatic?
I have tried it (thinking the same thing). Last time I was out I had a good run around on the aux to burn up the six month old fuel, and during that I wondered if it would help the speed if I pulled the main engine up. Main up or main down made very little difference to the speed - maybe a quarter of a knot tops. You can compromise and tilt the main up so there is just the skeg trailing in the water, and you still have most of the useful steering input but a bit less drag.
I think aerodynamics say that wind resistance increases as the square of speed (which is why you need a lot more power to get a bit more speed), so if hydrodynamics are the same, that would explain it.
You can also spin the boat on the spot by using the aux full ahead and the main slightly astern, yes it was a nice day and no I had nothing better to do than pretend I had real twins
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A Boat is a hole in the water, surrounded by fibreglass, into which you throw money...
I have tried it (thinking the same thing). Last time I was out I had a good run around on the aux to burn up the six month old fuel, and during that I wondered if it would help the speed if I pulled the main engine up. Main up or main down made very little difference to the speed - maybe a quarter of a knot tops. You can compromise and tilt the main up so there is just the skeg trailing in the water, and you still have most of the useful steering input but a bit less drag.
I think aerodynamics say that wind resistance increases as the square of speed (which is why you need a lot more power to get a bit more speed), so if hydrodynamics are the same, that would explain it.
You can also spin the boat on the spot by using the aux full ahead and the main slightly astern, yes it was a nice day and no I had nothing better to do than pretend I had real twins
How are you mounting your Aux Steve?
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Andy
Looks Slow but is Fast
Member of the ebay Blue RIB cover club.
I asked for my boat to be built with no rear lip on the transom, so mine is fitted straight onto the transom. I had to mod the engine mount to make it fit as the Vipermax transom is just too thick to slide the Merchatsu saddle over. After a bit of head scratching what I did was to carefully cut off the two round cupped washers on the clamps and replace them with flat washers which locate onto the stepped ends of the clamp screws, this just allows space to slide the saddle over the transom. I could have either altered the transom or the saddle but didn't want to do either, so this seemed like the best idea. It's a fiddle to mount the engine as you have to slide it on and then slide the washers in afterwards, but as I leave it on the transom all the time this doesn't really matter.
Only photo I have with the aux in is attached, but can get closeups tomorrow if you are interested.
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A Boat is a hole in the water, surrounded by fibreglass, into which you throw money...
So you run it with the Aux on the transom and tilted then? I thought about this but was concerned about damaging the Aux bracket when wave hopping. I was thinking of a stainless bracket that slide up and down, keeping the outboard in the vertical position.
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Andy
Looks Slow but is Fast
Member of the ebay Blue RIB cover club.
Interesting thread as I have just gone through all this ! (after 1st break down ever! )
Went last week to buy an aux and really liked the honda air cooled 2 HP 4 strokes at only 27lbs ! Easy to stow anywhere and just throw onto the transom when needed.
However not going to make much headway against any wind or tide.(not that we get much here)
But went for a nearly new mercury 4hp long shaft, 4 stroke instead .
But at 45lbs, hate to keep it permanantly on the transom.
So made a bracket on the front of the two pod seats ,right behind the helm.
Keeps it upright and out of the way and puts the weight forward.
When needed, I drop it on the back and as others said,lock it and use the main for steering. Not very responsive, but gets you there safely!
Gave me about 4.5 knots wide open. Not great, but hopefully avoid the ambarrasment of calling for help to my buddies on HMS Surprise; as I did last week ( Here she is dropping by with some oil ! )
Can't imagine keeping an aux on the back all the time .Seemed to bounce around everytime I went airborne, even when locked
cheers Dal
So you run it with the Aux on the transom and tilted then? I thought about this but was concerned about damaging the Aux bracket when wave hopping. I was thinking of a stainless bracket that slide up and down, keeping the outboard in the vertical position.
Andy, I had this set up on my old Viper 5.25... Never had a problem with the bracket despite plenty of days out wave jumping...
I used a little ratchet strap from the leg down to the bar across the bottom of the saddle to hold the engine down tight on the bracket so it could not flip up...
With regards to the lip, I spoke to Mike at Witton Glass Fibre and he said it was fine to just cut away flush to the top of the main transom as there is no wood in it so I used an angle grinder with a stone cutting disk fitted and it was absolutely fine.
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Chris Stevens
I had the same problem with an auxilliary on my last boat (Zodiac Pro). It couldn't be fitted directly on the transom as the Pro had a lipped edge nearest the tubes. In the end I fitted a Plastimo stainless-steel bracket. It needed a little adjustment (cut one corner off of the fixing bracket) in order to move it as far to port as possible. Might be an issue with a heavier auxilliary, but I was fitting a 3.5hp Twatsoo 2-stroke. The Kate Moss of 2-strokes. Smokes a little but squeezes in anywhere! Only 13.5kg in weight.
The only drawback with that set-up was the bracket used to rattle like a toolbox. Underway, the auxilliary engine could be tilted up and then secured with a ratchet strap to the back of the bench seat. It was practical enough.
Last year I bought a new RIBcraft 4.8m... then wish I'd kept the Twatsoo, which I'd sold a few months earlier with the Pro.
Luckily the new boat has a relatively wide transom, has a 60hp tweaked to 70hp Twatsoo 2-stroke main engine, and space either side. I opted to go for a light-pole rather than an A-frame, more because of storage issues rather than practicality.
I wanted another 2-stroke auxilliary so opted this time for a Mariner 4hp. Completely stripped it down, new impeller, cleaned fuel tank, carb, fuel pump, renewed starter rope, spark, etc. Runs like a dream. Although heavier, it was mounted straight on the transom. There's a towing eye on the transom, but the outboard bracket fitted over the top. The steering cable for the main engine is tight next to the auxilliary, but works fine. I knew I'd have the same problem with a rattling auxilliary, so I fitted a stainless-steel U bolt on one of the transom legs, to secure it with a ratchet strap. This is essential in my opinion.
Hopefully these pictures illustrate a few options. Basically, there's always a way to fit an auxilliary engine. It might not be pretty or practical in every scenario, but the knowledge that you have a back-up engine is what it's all about.
Andy, I had this set up on my old Viper 5.25... Never had a problem with the bracket despite plenty of days out wave jumping...
I used a little ratchet strap from the leg down to the bar across the bottom of the saddle to hold the engine down tight on the bracket so it could not flip up...
With regards to the lip, I spoke to Mike at Witton Glass Fibre and he said it was fine to just cut away flush to the top of the main transom as there is no wood in it so I used an angle grinder with a stone cutting disk fitted and it was absolutely fine.
Thanks for the info Chris. I'll bear it in mind whilst deciding/designing the mounting system
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Andy
Looks Slow but is Fast
Member of the ebay Blue RIB cover club.
Went last week to buy an aux and really liked the honda air cooled 2 HP 4 strokes at only 27lbs ! Easy to stow anywhere and just throw onto the transom when needed.
However not going to make much headway against any wind or tide.(not that we get much here)
I read somewhere a while ago - forget where - that the small aircooled engines are no use as an aux because they overheat slugging away pushing a big load. No idea if true or if it is a major problem but worth checking?
The Merc tilt support is not very strong - I used to use a small ratchet strap to tension it against the bracket but it is quite bendy and after a while I didn't bother with it.
Kate Moss of 2 strokes
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A Boat is a hole in the water, surrounded by fibreglass, into which you throw money...
It also has an extension throttle/steering arm so you can control the steering and throttle when you are further up the boat 
. 
Sula
