Excel Volaire 390 build thread

[Pikey Dave]

This came today, it sort of contradicts everything I hold dear about anchors, but we’ll give it a go. It’s certainly more SIB friendly than a metal anchor.

[jeffstevens763@g]

Originally Posted by Pikey Dave

Cheers. There’s about 3/4” clearance between the tip of the prop blade & the underside of the AV plate, so a 10 1/4 might just fit, depends on the splines. I might pick up a tiny tach just until I get here tuned in.

dave your very welcome to try my prop its 10 spline but for £42 for a new one is it worth the risk. link below where i bought mine from

https://ssimarine.co.uk/collections/s-propellers

[beamishken]

Originally Posted by jeffstevens763@g

you need a tach then really but my prop at 10 1/4 gives you equivalent to 2 inches of pitch more theoretically but an inch on diameter is too much for clearance IMO its here to try if required

Im intrigued to know how an inch on the diameter equates to 2 inch of pitch? My understanding was the pitch was the distance the prop moved forward per rev & the diameter increase or decrease gave more or less grip & any gain from increasing the diameter would only come from a reduction in slip which may or may not be a factor depending on installation.

[jeffstevens763@g]

Originally Posted by beamishken

Im intrigued to know how an inch on the diameter equates to 2 inch of pitch? My understanding was the pitch was the distance the prop moved forward per rev & the diameter increase or decrease gave more or less grip & any gain from increasing the diameter would only come from a reduction in slip which may or may not be a factor depending on installation.

In terms of RPM Dave would know what I meant

[beamishken]

Originally Posted by jeffstevens763@g

In terms of RPM Dave would know what I meant

I'm genuinely interested in how this works could you explain? Every days a school day

[jeffstevens763@g]

Originally Posted by beamishken

I'm genuinely interested in how this works could you explain? Every days a school day

An inch of pitch = 150-200rpm up or down not an exact science but a guide
An inch of diameter = 2 inches of pitch in terms of RPM loss or gain.

So the prop I have would give Dave an RPM drop because in effect it would be like a 14 inch pitch prop more surface area on diameter than on pitch.

It's a rough guide in some circumstances pitch can drop 400-500 RPM although it's never happened to me I guess it's when your right on the limit of ideal RPM range

[GuyC]

Dave Gerr's propeller handbook provide some rules of thumb and the pitch diameter relationship is one of them.

Paraphrasing it - "One inch in diameter absorbs the torque of two to three inches of pitch. Both pitch and diameter absorb torque but diameter is the most important. It's only a rough guide."

Diameter is apparently the biggest factor in determining the amount of power the prop can absorb and therefore the thrust it can produce. The other factors are RPM and pitch.

It's all very interesting but I think I'd have to live and breathe prop's for some time before I understood it.

[beamishken]

Ok seems I've been under the misapprehension that for a high speed application (planing hull) that the diameter variation available within a gearbox size range meant that in terms of prop selection the diameter was all but irrelevant. The pitch has always been the focus when selecting a prop for best rpm v speed.
Most prop catalogues give very little option in terms of diameter as most seem to offer finer pitches with larger diameter and as the pitches increase the diameter decreases within a small range, i had assumed the reason being that a larger blade area created more drag and therefore efficiency suffered as speed through the water increased.
I wonder why manufacturers don't offer more choice of diameters if the diameter has such a large influence on the final result?

[jeffstevens763@g]

My apologies to Dave for going off topic.
When I had my rib it had a 14x19 Ali prop I got a 131/2 x 21 ss prop in terms of top end speed both were the same ss is suppose to be 6% more efficient too so when you look there's a big difference between sizes going down 1/2 inch on dia gave 2inches more pitch for the same RPM having said that at the time of testing each prop conditions might not have been the same, lots of factors come into it and no two boats would be the same.years ago I bought a yam on the Isle of Man I was lucky enough to trial various props by the guy who supplied and fitted the engine he said at the time until you try you might never get it spot on

[beamishken]

Yeh sorry for thread drift I wonder if the mods could split off the prop chat so it can be continued elsewhere?

[willk]

Originally Posted by beamishken

Yeh sorry for thread drift I wonder if the mods could split off the prop chat so it can be continued elsewhere?

Careful you don't drop that bone...

[A1an]

Originally Posted by Pikey Dave

Attachment 131575

My OCD meter is off the scale!

Don't tell me you didn't have 3 matching stainless bolts in that shed of yours.

Cracking job otherwise.

[Pikey Dave]

Originally Posted by A1an

My OCD meter is off the scale!

Don't tell me you didn't have 3 matching stainless bolts in that shed of yours.

Cracking job otherwise.

It did originally have matching bolts, but then I needed 2 longer ones to attach the battery pack. I try not to look at it[emoji849]

[GuyC]

Hillarious - I had exactly the same thought but decided as they were different lengths, you could possibly get away with it.

The slots could have been aligned though.

[Pikey Dave]

Long time no see, been busy & the weather hasn’t been conducive [emoji849]
Anyway, a bit more work. I picked up a Milpro fuel bladder off eBay (thanks for the heads up @spartacus). A Parker 2 micron filter/separator on a removable mounting plate & a Railblazer rod holder now joins the ensemble.
New grab lines fitted to replace the tacky plastic braided ones.

[jeffstevens763@g]

Very nice like the bladder Dave will all the stuff on tbe transom have to come off during transport when its folded up

[Pikey Dave]

Originally Posted by jeffstevens763@g

Very nice like the bladder Dave will all the stuff on tbe transom have to come off during transport when its folded up

Yup, but it’s only 2 wing nuts to remove it.

[benhben]

Hi, just reading through this thread with interest. Do you bolt your motor to the transom in addition to the standard clamps?

Ive read a few posts stating you should really, but ill be packing the boat up at the end of each session and am loathed to drill into the transom if not needed.

On the other hand I've just bought a new 15hp Tohatsu 4 stroke for use on a 3.4m sib and dont want to risk losing an expensive new motor.

Ta
Ben

[jeffstevens763@g]

Originally Posted by benhben

Hi, just reading through this thread with interest. Do you bolt your motor to the transom in addition to the standard clamps?

Ive read a few posts stating you should really, but ill be packing the boat up at the end of each session and am loathed to drill into the transom if not needed.

On the other hand I've just bought a new 15hp Tohatsu 4 stroke for use on a 3.4m sib and dont want to risk losing an expensive new motor.

Ta
Ben

Don't drill anything in the transom unless your going to seal the holes I would just have a lanyard on the engine to a secure place and make sure the clamps are tight and fasten together with a bit of rope too so they can't spin

[Pikey Dave]

Originally Posted by jeffstevens763@g

Don't drill anything in the transom unless your going to seal the holes I would just have a lanyard on the engine to a secure place and make sure the clamps are tight and fasten together with a bit of rope too so they can't spin

^^^^^^^^
Wot he said.
I just use the clamps & have a lanyard to an eye bolt in the transom. The eyebolt is one of the fixings for the transom wheels. All sealed with Sika 291.