and now for something completely different!

[Sandro Picchio]

Jon,
I perfectly understand and sympatize with the lack of room for all our "toys" and children's (and grandchildren's for me). And also the look.
I am afraid it is hopeless, because as soon as you, anyhow, get more room, say a new garage, a larger courtyard or any, in an eye-blink it is full of gear and you are again longing for more room.

Enjoy the age of working and making projects together with your teenager children . It's a very good period of life.
All the best

Sandro

[headdownarseup]

Thanks Sandro.

It's not always easy being a dad, but we do what we can with what we have to hand.
This project is just my response to a question asked by my nearly 12 year old son. "Could we go a bit faster just by using a slightly bigger seagull"

Sounds simple enough doesn't it!

The fun part is finding out. Trying different things. Seeing which works best on our little inflatable and remaining faithfull to the seagull brand.
There might be some eyebrows raised along the way, but it's all good. It's nothing serious, just a bit of fun.

Jon

[headdownarseup]

So
Streamlined gearboxes.
Many different ways this could be done, this is my interpretation of what a streamlined gearbox could look like. A couple of afternoons worth of work in this, but i'm fairly happy with the overall appearence. All the underpinnings of the original gearbox design are still there, just covered up a bit here and there.
I reckon this 40 bitsa is going to need all the help it can get, so i'm looking for inspiration elsewhere to at least help things along the way. It might make a small difference, but small differences all add up in the long run. The added bonus is that it still comes apart easily for that all important cleaning and maintenence. Just waiting on some new gaskets right now, but i'm going to call the lower end finished.

It's been said before that i could have easily used a century powerhead with a featherweight gearbox, but it's been done before. I like to be different.
Not that much mention of these little fellas being "stretched" to their limits, so i thought i'd have a go and see where it leads us. Nothing serious just a bit of fun.
Please bear in mind that my 12 year old son will be piloting this "contraption" when it's finished, and with this in mind i thought better to start small so he can gain some experience before stepping up to the bigger motors.

As this is a Bitsa there are no rules to anything. I'm builing this to mine and my son's specifications and nobody else's. A helping of artistic licence too. I hope you like what you see, and that it's not too scary as some of the "franken motors" we've seen before.

More coming soon

Jon

[headdownarseup]

Some of the parts that i ordered have arrived today, so the gearbox will get finished tonight.

Next job is the powerhead.
I've found that the crankshaft assembly i wanted to use was bent. Not by much, but enough to pinch in certain areas. As i dont have a lathe to double check its straightness, the easier option for me was to buy another crank.
Not wishing to let too much out of the bag here, but i can tell you i've offered up several prayers to the gods of speed and power and surprisingly the gods have smiled on this little chick.
Full speed ahead now as canal testing time is fast approaching in less than 3 weeks from now.
I'd better get my skates on!

More soon with some pics

Jon

[Hugz]

If you wish to please your son in the inflatable with more speed why not take him out wave riding? An inflatable is ideal as they are so stable. Or find a big stink boat and ride his wake. You will be amazed at the speed you will get up to and the exhilaration of surfing the wake. Even an inflatable with a forty can flip, so practice on smaller wakes first. After a few scares you will know when to back off. You might have to travel a bit from Bristol.

[headdownarseup]

Funny that Hugz, last year i went out from Poole in my mates 14 foot rib with a 40 Yam on the back. Not knowing what to expect i thought i'd wear a full set of waterproofs to be safe.
Good job too, as he must have chosen a pretty rough day for going out. Waves in the harbour up to 4 feet, but out in the open more like 10 with quite a swell with it. Airbourne doesn't quite describe what we went through on more than one occasion that day. Battered and bruised for a few days after.
Good fun though if a tad dangerous, but wont be doing it again for a while.

This little project of ours isn't quite going to be put to such extremes however, more quiet canals where we can both annoy the gin palaces that moor along the towpaths.
Although i have been made aware that i'm first in line for a 15hp mariner that might be up for grabs soon provided the price is right. That'll go well on the back of this Zodiac.

Jon

[headdownarseup]

Gearbox is all buttoned up, quite happy with how things are at the moment. No unusual noises from inside the box despite not having any oil in yet.
Goes in and out of gear nice and smooth with a satisfying thud!

Choice of prop is a bit limited with this, although i do have another option i'm having a little look into. Might not be the obvious choice either. But a "bitsa" doubles up as a R&D testbed for something else. Sounds a bit "skunkworks" doesn't it?

Powerhead is fully assembled (pics later) with a healthy 100psi of compression which puts it about where i was expecting it to be. Fairly typical in fact for a 40. Other mods have been done as well, but i'm not willing to share at the moment for fear of being shot down in flames by the "headmaster".

I just need to order a small tachometer for some further testing and we're nearly ready to head out onto the water.

The fuel tank will get a quick paint job this weekend and that should be us done and dusted.
I fully expect to be going back and forth "adjusting" and "tweeking" props along the way to find out the best acheivable overall performance from this rig, so bear with me.

Jon

[Oyster 49]

Do share...

I would suggest a cheap tacho and a GPS to compare speed and RPM. If you have a clutched 40 and have improved the power, try a direct drive 40 prop. It is a coarser pitch and with a stronger pwerhead you might just be able to drive the coarser prop, and thus drive the boat more at the same RPMs. If you have a standard prop the improved powerhead may over rev.

[headdownarseup]

Nothing sinister with any of this really, all pretty basic stuff that anybody could try at home with a few basic handtools and some time to kill.
A cheap chinese tacho from ebay is what i shall use for measuring engine revs, and i have a gps app on my phone which conveniently measures speed.
You and i must be thinking on the same wavelength when it comes to props Adrian.

I've been doing some number crunching with both of these props i have (the original 3 bladed and a direct drive 4 blade hydrofan) and for a theoretical and dirty measurement so far the hydrofan seems to be a winner. Whether or not i can manage to maintain the engine revs with which to spin this prop remains to be seen. Then there is slippage to take into account (still trying to get my head around this at the moment) but very roughly 18% seems to work well enough so far in my calculations.

I wont blind you with the science behind this as you'll easily be able to see on various other websites just how to calculate various bits and bobs on props.
Using one particular website as a reference i've taken some dirty measurements with both props and found the 3 blade has a pitch roughly speaking of 9 inches (better for engine revs) whereas the 4 blade pitch works out to 11 thereabouts (better for overall boat speed)There are plenty of variables with both these props, but theoretically speaking the hydrofan would appear to be a tad "quicker". Also the 4 blade has a different diameter to the 3 blade which will change things around a bit and potentially slow the engine speed ,so i might have to remove some metal to compensate for this.
As for over revving the engine i doubt if it will go much past 4500rpm (more likely to be a bit less nearer to 3800-4000) but we'll see soon enough.

This is the dangerous bit, if i've done my measurements correctly and tidied things up , in theory a boat speed of around 12mph (just under 11 knots) could be possible which would make this bitsa nearly twice as fast as the featherweight its replacing. Even if it's not quite that quick i'm still aiming close to 10mph as a benchmark figure. And then there's the boat itself which is whole different ball game .

All theory of course but in the next couple of weeks i should have some better numbers to put together.


Jon

[headdownarseup]

IT'S ALIVE !!!...

Had a spare 30mins this afternoon so i thought i'd see what would happen.
1 pull on the rope from cold and it was away. (i really must change the water in my bin)
I think i'm running a smidge rich at the moment as the little chick is still 4 stroking a bit even at near full throttle.
I have 2 options in the carb, either go with a 10:1 set up or a leaner/greener mix at 25:1 and play with the mixture screw to suit.
I'm using a late model villiers carb (in black with all plastic bowl and cowl) but with some of the fittings being swapped out for older polished brass parts. Looks odd but at the same time different. (no rules remember)
No dramas, no overheating, all fairly normal stuff just a tad rich.

Compression measured again after a run and holds steady at 99psi (happy with that but still room for improvement if i need it)
Points and plug will get another going over this evening to make sure it's as good as it can be. Just thought of something else i could do whilst i'm in there (shhh)

Might have to look at the flywheel balance again as it feels a bit "lumpy" when running in the bin.
Bought the paint to do the tank, but as it's a tad fresh outside i'll leave it till tomorrow.
So far so good.
On target for the 20th of this month.


So, this evening it's prop study for me as there's nothing on tv!

More soon

Jon

[Hugz]

Just being the devils advocate but if your inflatable is ten foot long its theoretical max hull speed is going to be 4.2375 knots. A bigger motor will chew more juice and change the angle as your vessel tries to climb up its bow wave but no increase in speed or am I missing something here? Have a read of this (left click then left click again)

Interestingly when I was a kid of about 12 (1968) and weighed little more than a grasshopper (approx 7 stone) I used to zip around in a 10ft tinnie with a johnson 4hp twin which easily put me on a plane. Would a curlew have the same thrust? I never did flip it but came close a few times .

Nothing on TV, yay, 102 registry time

[headdownarseup]

Just working through the theories at the moment Hugz.
Nothing finalised yet, but i get your point with large versus small motor.

The boat is yet another dimension to all this. Again some stuff i'm working through.
I'm thinking i might have to carry out some clever alterations to the hull in order to get somewhere close to what i'm aiming at.
Trial and error with a lot of this (mostly error at the moment) but there is a glimmer of hope.

As a baseline figure using the featherweight as an example, best speed indicated was 4.5mph bearing in mind this engine is basically bone stock.
The boat leaks an alarming amount of water inside so becomes quite heavy as a result with hardly any wake to speak of so i don't think i was quite up to hull speed. Keep the water out and i might have a fighting chance with this.
The bitsa hopefully will have a little more power with not too much increase in weight so with any luck the angle of attack shouldn't change that much either. Allowing for poor hull shape and design i reckon i can do something with this rig a little better than 4.5mph by way of some trim tabs at the back thus adding some length to the hull of around 12 inches (still going over some numbers with this)
Did i mention the boat has an inflatable vee section to it.


102 data is nearly finished, so next few weeks and i'll post it up, but for the moment i'm taking a small break from it in order to do this little project.

and there's still nothing on the telly!

Jon

[Hugz]

by way of some trim tabs at the back thus adding some length to the hull of around 12 inches

That's is an interesting concept. Make up the transom bracket to sit a couple of meter behind the boat and fill up the gap with boat wide trim tabs... good thought.

and there's still nothing on the telly!
I thought TV's where things of the past

Jon

[headdownarseup]

For the moment i'm trying to get the engine to produce more power than was available back in the day. My theory is that if i can get the engine to produce higher revs without destroying itself and still remain reliable, then a bigger prop (slightly re-worked) can only help with pushing the boat along a little quicker than before. (Almost the same as your old advert Hugz)
The boat itself isn't the best type of hull for this application, but i'm looking down every possible avenue for something that might work a little better than it does at the moment.
Nothing too drastic mind you as this inflatable still has to pack away into its bag for storage. If i go with the trim tab option then these will have to be removable with ease, a simple bolt on bolt off option. And then there's the water leaks to deal with!


Any how, gave the little chick another run in the bin today after sorting out the 4 stroking. Now runs pretty good. Flywheel still "feels" a bit lumpy so i'm looking into altering the balance with this.
I tried the hydrofan prop too. I noticed a drop in revs (which i was half expecting) so i'm going to trim the blades down a smidge little by little heading in the direction of the 3 bladed dimensions. Balance will get checked along the way. Every little bit helps, and this little one is going to need all the help it can get, and from wherever i can find it.

My youngest son has a lot to answer for! (i was quite happy with going slow as well)

More soon
Jon

[headdownarseup]

Well, that was easier than i was expecting!
Flywheel now balanced fairly neutrally. Happy with that i must say.

Prop is another matter. I've decided on 8 1/2" as being a usable/workable diameter for now. On the water testing should show up any shortfalls with this, but for now at least it's all heading in the right direction. I'm aiming for a ballpark wot figure of 4000rpm. A bit more would be better, but not knowing how much power or sustainable revs the engine will eventually make i'm playing things safe for now. Tachometer now on order so when that arrives it will be into the bin for some more testing.
All 4 blades are now trimmed up nice and tidy, now for some balancing and polish.

Weather is still a bit on the cool side for painting, so the tank is taking a back seat for the moment.

Jon