Todays Boating

[Ray Wood 3Participant @raywood3]

Hi Ash,

The weed is strong this year !! must be the heat making it grow 🙁 my friends at other clubs in the south east are all having the same problems !!  Our yacht racing course is becoming smaller every day, at Bluewater which is fast turning into Greenwater 🙂

Have a great holiday 🙂

Regards  Ray

[Philip OxleyParticipant @inonowt]

Hi all.

Had a great day boating yesterday. Had all boats out and ‘Altair’ (MTB379) had its 1st outing. Lots of admiring looks and positive comments. It went really well and it’s is so quiet. It a bit low in the rear but other than that, no issues. Maybe a bit too much rudder. Moreover, what I was most pleased with was, ‘This is it’ finally (thanks mostly to Chris Fellows help and advice last year) got up onto a plane and behaved as I’d wanted to. Also on its 1st outing was a wheeled trolley, making it easier to transport boats to and from the car. No mishaps and no breakages, so all in all, a great day.

Best wishes

Philip

Philip

[ashley needhamParticipant @ashleyneedham69188]

Well done Phillip.  Good snaps…perhaps move the battery forward a bit?? Sometimes planing boats have to be a bit down at the bow yo sit properly at speed.

No boating now for 3? 4? Weeks due to hols and weed. By all accounts the weed is down a bit but now the pond is very scummy…

Tricky project..not much movement, but the next project after tjis tax been identified, a follow-on if you like from something started 15. Years ago but never got working, namely an SRN1 which was a whopper and made out of vacform parts for which I have the tools for still! It was always ambitious but mainly just far too big and thirsty on the batteries.

The new one will be 2/3 size and only have one motor ( the other had ducted fans in the ducts plus a lift motor).but only AFTER I finish the other one…

Skid boat in next mag…something i struggled to get to work. Unfortunately Lindsey made me to cut the wordage down and so the tale of the puzzling and epic struggle has been neutered but there we are.

Ashley

[Philip OxleyParticipant @inonowt]

Hello Ashley.

Thanks for the reply.  Since the photos, I have rejigged the internals and moved the battery forward and fitted it lengthways along the keel line.  The drawings show it a little forward from where I had it. I noticed this when looking at them as I’m intending to use a modified version of this hull for a motor yacht.

There is another issue I have which I’m not sure contributes to the low back.   When installing the drive lines, after getting a good line I fitted the A frames first but they must have dropped 2 or 3 mm during installation as subsequently I had to pack up under the motors with 1.5mm ply.  The drive lines are good but are a little steeper than I’d intended. I get the feeling this has increased the plane angle.

I bought some led lighting which I’ve retro fitted into the bow behind the portholes.  More for the challenge than anything else.

Not having CAD I’m using pencil and paper to draw the motor yacht.  It’s going to be a MCY70 or 76 hopefully but I’m still trying to figure it all in my head.  I have some pictures which will enable me to achieve some sense of scale, and being 70 or 76′ long this hull (modified) lends itself quite nicely.  Anyway, we’ll see.

Best wishes

Philip

[Chris FellowsParticipant @chrisfellows72943]

Glad to have been of help Philip and that the models are now performing as you wanted. I don’t think that the prop shaft angle is why the stern runs low. If anything the steeper angle should raise the stern as the hull will pivot at the point the hull is out of the water. How does it sit at rest? If a little bow high you could try some ballast towards the bow.

But looking at the last photo your model doesn’t have a lot of freeboard at the stern and I think it is just dropping into the hole that occurs when a boat is not fully on the plane. It just looks a bit dodgy! I take it that at rest and slow speed it sits higher on the water? Higher speed may raise the stern?

[ashley needhamParticipant @ashleyneedham69188]

One trick is to add a shelf to the stern. This effectively lengthens the boat, moving the centre of gravity and helps in stopping stern sinkage ( inevitable with old sge).

A temporary one affixed with tape will suffice for a quick test.

Ahhh…arguments about prop angles…I could throw in prop lift here…some props generate more lift than others. Might be worth trying a few different props and even reversing the direction…

Took the old SRN1 to Trevors and decided to fix the motor issue and re test it. I spent a considerable effort on this…what with the substantial mdf tools for the vacforming and the myriad half-round styrene rods to replicate the originals ribbing. I layer fitted it with a higher 2200kv lift motor but never fixed the side thruster ducted fan units ( one stopped working last time our on tne pond) to retest on water to guage the effect of the extra lift so don’t really know if it will make a lot of difference.

I may still make a smaller 1, powered by a single motor and using bleeding off air to.propel it, but it won’t be a full hoverer..mor?e like an “assisted skimmer” as i fancy finding out how well it would go.

I have built a lot more stuff since the original 1 and would do it a bit  differently second time.e. snaps to follow.

Ashley

[ashley needhamParticipant @ashleyneedham69188]

Cycled to the pond and was staggered to see that its completely clear of weed!!!  Amazing…where’s it all gone?

Ashley

[Colin BishopModerator @colinbishop34627]

Cycled to the pond and was staggered to see that its completely clear of weed!!! Amazing…where’s it all gone?

Washington DC I expect…..

Colin

[Philip OxleyParticipant @inonowt]

Good afternoon all.  Thanks Ashley and Chris for your replies.

Your comments, Chris, prompted me to look at the Barrie Griffin video of the model, and some pictures on the internet.  BGs model is also quite stern down, but the real-life pictures not so much, so I’m thinking it’s just the way the way the model is.  You’re right, there isn’t a huge amount of freeboard at the back and the deck is kind of at water level at full speed.  The brass A frames and brass propellors would add weight and I did use a substantial amount of P38 to fix them in.  Possibly 40-50gms in all.  I’ll note the ‘at rest’ level nest time since I don’t have a bath to do that.

The shelf idea is interesting.  Accepting what you say Ashley, it would also act like trim tabs available in the market, but temporarily taping a piece of ply, or perhaps even wing trailing edge (to give some lift) to overhang by an inch(ish) would be a good test.  And as Chris says, I can add weight at the front too.

Interesting what you say about prop lift.  The props are 3 bladed brass from Howes with the starboard rotating clockwise, and the port anti clockwise.  I can swap them over and change the motor’s directions, which is what I think you’re suggesting.  I tend to agree with Chris, tho I could see and argument for the thrust going to the front of the boat, there by lifting it.  Maybe I’ll try smaller nylon props.

Pleased to hear your pond is weed free Ashley.  Ours, while free of weed, has a fair bit of floating twigs, leaves etc. which foul the props somewhat.

Thanks and best wishes to all.

Philip

[ashley needhamParticipant @ashleyneedham69188]

Philip.

In my experience…

Outwards turning props tend to push water up between them. This can be very helpful for single rudders boats as you get a bit more water flow over the rudders.

Inward turning props tend to.push water down. That’s a bit of a black and white statement I suppose but there is a sideways component to the thrust of a prop besides churning

You also  get effects of turbulence etc at the blade ends which cuts down efficiency. One of the reasons kort nozzles are more efficient for lower speed work is that the turbulence is contained by the ring. Similarly for ducted fans..a close tolerance between blade and fan is a must.

I read a good article years ago and it  said an X two bladed prop was a really good general purpose high speed item and would propel almost anything quite efficiently. Not the best perhaps, but better than most and really cheap. Certainly better than a standard sort of three blade brass one for high speed work.

The lower pitched S types are probably better overall unless you want to go very fast, but the bigger X variety are very good for low speed applications, a bit counter intuitive perhaps.

A shelf is different to a trim tab, as there is a gap between tabs for water to rise up, lowering the lengthening effect.

Ashley

[ashley needhamParticipant @ashleyneedham69188]

Picture of the new 60mm prop Trevor has just bought off Ebay for a tenner for his Flower Corvette which we are tittivating for display at the Royal Egham show at the end of August. It currently has a an X50 prop with a 2.5:1 geared 850 on 12v. This powers the 2m (!) boat very well but doesnt look so good. It’s sooo heavy!

It looks wonderful…but…

It’s not brass, its a cast zinc alloy, and plated a gold colour. Thete is a plain 4.1mm hole and oddly a dog drive.

However…it looks fantastic and will tap out to 5mm.

Ashley 

[Colin BishopModerator @colinbishop34627]

The boat will obviously now turn in a more polished performance….

Colin

[ashley needhamParticipant @ashleyneedham69188]

Ah Colin…..

Bumper boats for Sunday. They have not been out so far due to various combinations of weather and weed. Should be a fun morning.

• Wet’n’dried the bottom of Trevors corvette on Tuesday to get rid of some of the resin runs and so on (boat was built in a hurry originally trying to meet the D-day event deadline)  and repainted it black. Looks so  much better..just 40 mins hard work ( in the sun).
• Ashley

 

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