E-TEC prop.........

[BogMonster]

Hi all

I have a 21" Viper prop on my E-TEC 150 (Vipermax 5.8).

It has a bit of minor damage here and there which has been sanded out carefully (just very minor nicks in the leading edge - mainly from picking up small stones when launching).

I have noticed over time that it is getting more prone to break out and cavitate when you accelerate hard with the helm well over - even when it's trimmed well in.

Would a 4 blade prop help with this - and what would be a good (safe) option? Due to location, trying different props is not an option so it would be a one time purchase.

[jeffstevens763@g]

hi mate not an expert but something has changed if you were propped properly in the first place. i would talk to someone like steel developments Home page tel 02088747059 fax 02088779537.

hope that helps

cheers

[Chris]

Hi Stephen, what are your RPMs at WOT and speed ?

[Hightower]

Hi Stephen.

I've probably got the most similar set-up to you, Vipermax 6.2 (Out of the same mould as yours) and a 150 Evinrude DI. Now you have to bear in mind my RIB is heavier than yours and my gearbox ratio might be slightly different to yours but I've been running a standard Viper 19p prop most of the time I've been running my RIB. It did come with a 21p viper but it wasn't getting up to the recommended WOT revs.

Once set-up I've never had breakout or cavitation/ventilation on hard cornering and my prop has had similar small chip damage as you are describing. I've recently tried a 17p Viper and with impressive holeshot and only down on max speed by a couple of knots. Again handling is superb but fuel consumption is significantly higher.

IMO I reckon that you were on the edge of what you could get away with on the engine height. A bit of damage on the leading edge of the prop could be enough to drag air down when on the limit and cause ventilation during hard cornering. If you are confident that your prop is okay I would be lowering your engine height by a bit and see if that sorts your problem. If you are after another prop I would be looking at possibly going down to a 19" (depending where your WOT is now), if that doesn't quite do the trick in the high performance stakes, you'll have a rough water prop and also a useful spare too.

[Searider]

Was the prop good when it was new?

If it was then the prop is damaged in a way that's degraded its performance - perhaps it's out of balance or a blade is slightly bent - which you might not see.

If the prop was good when new then you need to either get that one refurbished or simply buy the same again - I appreciate that distance might be an issue for you!

[Pikey Dave]

I've said it before & I'll say it again Mercury Rev4.......

[Mollers]

Originally Posted by Pikey Dave

I've said it before & I'll say it again Mercury Rev4.......

Pardon.

[Pikey Dave]

Originally Posted by Mollers

Pardon.

Ah now! Are you being subtle or ironic?😄

[jambo]

Originally Posted by Pikey Dave

Ah now! Are you being subtle or ironic?😄

No dave just obstructive as usual, obviously on the holiday juice tonight

[Mollers]

Originally Posted by jambo

No dave just obstructive as usual,

Is Gaelic your 1st tongue?

[jambo]

Originally Posted by Mollers

Is Gaelic your 1st tongue?

No cànanan Goidhealach, actually

[BogMonster]

It was never perfect unless trimmed right in. The engine height is OK, the issue is that the helm seat is well forward, and when you're 1 up with full fuel it is a bit heavy in the bow, and er may have got a bit heavier in the last five years - it's better with all the seats full.

I made a mistake - it's actually a 19" Viper not a 21. It doesn't get to full revs and never has - I think again it is because the bow is lower in the water than a boat with the seating further back, as most are, but the get up and go is immense so I don't think there is any issue with the engine. However the balance is good for keeping the nose down in rough conditions, which is more important to me than flat out speed.

I suppose a need for more weight at the stern could be an excuse for twins

[Searider]

Maybe you need something with more bow lift, or more cupping.

We originally had a vengeance on our Opti which was prone to blowing out. Changed it for a Laser II and was a great improvement.

[Chris]

Originally Posted by BogMonster

It was never perfect unless trimmed right in. The engine height is OK, the issue is that the helm seat is well forward, and when you're 1 up with full fuel it is a bit heavy in the bow, and er may have got a bit heavier in the last five years - it's better with all the seats full.

I made a mistake - it's actually a 19" Viper not a 21. It doesn't get to full revs and never has - I think again it is because the bow is lower in the water than a boat with the seating further back, as most are, but the get up and go is immense so I don't think there is any issue with the engine. However the balance is good for keeping the nose down in rough conditions, which is more important to me than flat out speed.

I suppose a need for more weight at the stern could be an excuse for twins

If your looking for increased bow lift then a 19" Rebel would be my choice. As you are heavily loaded at the front, you could try dropping a hole on the current Viper however this may mean cutting the transom down if Roy had the transom height set to match the engine which would normally mean the engine is sat with the vent plate set about 2" above the bottom of the transom.

19" on 150HP for a 5.8 should be right on the money in terms of WOT RPMs.

[jwalker]

Originally Posted by BogMonster

It was never perfect unless trimmed right in. The engine height is OK, the issue is that the helm seat is well forward, and when you're 1 up with full fuel it is a bit heavy in the bow, and er may have got a bit heavier in the last five years....

Well that doesn't make sense. If you are heavy in the bow, trimming right in to make it ok would not be usual since that will also drive the bow down. We need more info.... When you say it was never perfect, what exactly do you mean? Did the prop break away when trimmed out a little?

[BogMonster]

Yes, basically that JW. The E-TEC has a trim % readout from 0-100. The sweet spot for cruising at say 25 knots is about 25% - 30%, when the boat is well balanced and the steering feels lightest. But you really need to be < 10% trim for any hard turns with significant throttle at low speed. And that's a pain because you need to trim in to do that and then trim out again as soon as you are back up on the plane. The steering is terribly heavy under power when trimmed right in.

Chris, the transom was ordered higher than standard to suit the XL shaft engine, with the intent being to stop the Atlantic coming in over the cutout as usually happens with long shaft engines when you are going astern (had it with the old Destroyer). So to drop the engine I'd need to start carving lumps out of it, and it isn't a serious enough issue to warrant that, nor am I confident enough in my GRP skills, nor would I really want to do it anyway. I'd need to measure the plate to be sure but I would guess than when set horizontal it's probably less than 2" above the planing pad.

I suppose if I'm being honest it's a slightly irritating problem, and if there is a prospect of significantly improving it by spending a few quid on a different prop that is a quick fix, I probably will. If the solution requires a lot of time or skill, I'll probably live with it

[Hightower]

I reckon that you should still lower the outboard. I had a concern with my installation on an xl outboard and insisted that the transom was made lower than Roy recommended. I'm pleased I did because my saddle is lower than the height that Roy suggested and I have fantastic handling with no breakout in any hard turns. BTW I run 4750rpm at WOT with the 19 and 5000rpm with the 17. Recommended rpm for the DI is 4750 to 5250

If you think weight distribution is an issue chuck a couple of bags of sand aboard and move them to where you think the imbalance is which in your case is towards the rear.

[OSPREY RIBS]

Originally Posted by BogMonster

I'd need to measure the plate to be sure but I would guess than when set horizontal it's probably less than 2" above the planing pad.

I suppose if I'm being honest it's a slightly irritating problem, and if there is a prospect of significantly improving it by spending a few quid on a different prop that is a quick fix, I probably will. If the solution requires a lot of time or skill, I'll probably live with it

If the plate is set at 2" that would normally be right for an E-TEC and you would normally not experience prop slip until you were trimmed over 50% on hard cornering. However as you have said having the weight forward is an issue as this will hold the nose down when you are trimming out causing the prop to ventilate. Dropping the engine would help, however a larger cupped blade prop like the Rebel will provide more bow lift so may be enough to solve the problem.

If you did want to drop the engine then taking an inch off the transom would clearly be your only option. Its not quite as scary as it sounds if you have the necessary materials and tools to hand.

Adding weight might help but may also cause other issues in terms of the balance as you come of the top of a wave etc.

If it were me then the first option would be a prop change as its the easiest first step. Drop me an email I may be able to get hold of an ex demo REBEL for you.

[jwalker]

Originally Posted by BogMonster

Yes, basically that JW. The E-TEC has a trim % readout from 0-100. The sweet spot for cruising at say 25 knots is about 25% - 30%, when the boat is well balanced and the steering feels lightest. But you really need to be < 10% trim for any hard turns with significant throttle at low speed. And that's a pain because you need to trim in to do that and then trim out again as soon as you are back up on the plane. The steering is terribly heavy under power when trimmed right in.....

Stephen, your engine is too high. There is a tendency these days to get the engine as high as possible and to play about with props, trim, blade types to make a sytem work but for general purpose use I believe this to be folly. It is not unreasonable for a anti-ventilation plate to be 25mm below the hull - yes, below! - there wouldn't be absolute maximum speed but you'd not be as far off as some folk would have you believe. The trim response would be better, the steering would be better, the load carrying would be better and rough water handling would be better.
I'm not suggesting you get the engine that low, just that it's not unreasonably low. Given what you've described in your postings over the years, for your seas I would be looking at the anti-vent plate being about level with the hull bottom.

Regarding props: in general, a prop with blades like teddy bear's ears is a good general prop but won't be too happy if it runs at the surface. A more raked blade is common nowadays but the blade sectional shape will make a substantial difference to it's performance.

If the blade is pretty flat it will be a kinda general purpose prop, adding cupping to the REAR edge will have the effect of an increase in pitch without the negative of actually increasing the pitch - a bit of free performance. (Kinda like putting down a bit of flap on an aeroplane wing - extra lift.)

If the cupping also goes around the tip of the blade, the characteristic begins to change. This cupping actually begins to form a crude spoon shape. Likewise, it's possible for the blades to be slightly spoon shaped - with or without cupping. The spoon shaping will give a blade a characteristic which is bow lifting (actually, it pulls the stern down) and it also produces a blade which will hold the water well when near surfaced. With careful design, spooning and cupping together can produce a blade capable of running surfaced where the top of the blade is actually out of the water. This might sound ideal and why aren't all blades like this!? Well, when you're next trying to get on the plane in heavy sea and your boat's bow is skyward, the last thing you need is a bow lifting prop!! And it can still be bow lifting when fully trimmed in - especially if it's already 50mm above the bottom of the hull!

So, take care if you go down the prop change as an easy fix - I doubt it will be.

If your present prop is very flat in section you may gain a little with a touch of cupping and spooning. You can do this to your own prop using a hammer if you're a bit brave. Since your present prop is now well used and you're considering a replacement you might feel it's worth a try. Make card templates of your original blade shape and modified templates of what you feel you'd like to acheive and set too - gently does it. You can add more if necessary or knock it back a bit if too much. I've done this a number of times with good success.

With regard to lowering your transom and flooding going astern, yep, it's a pest. But it's the way to go IMHO. You could build a section for catching the water in front of the engine to prevent it coming aboard, I'm sure you will have seen such arrangements. Or even a dummy transom so only the rear of the boat gets a flood and it then drains out of the trunks. A bit of creativity will produce a solution I'm sure.

PS: Just a thought, a spooned and cupped blade will give you a noticably softer ride in a head sea where you're travelling at a respectable speed and the boat is just about leaving the water. This is because the blades are capable of providing drive while they are only semi-submenged. If you combine this with a lowish engine mounting you've got the best of both worlds because the prop will be lower in the water too, ie. the bow will tend to be held up while the hull is hopping over the waves so preventing a beating each time it lands. Because the engine is low, bow lift when getting onto the plane tends to be negated to some extent when trimmed fully in.

It's all a compromise. Good luck with it.

[Hightower]

Originally Posted by jwalker

There is a tendency these days to get the engine as high as possible and to play about with props, trim, blade types to make a system work but for general purpose use I believe this to be folly.

The trim response would be better, the steering would be better, the load carrying would be better and rough water handling would be better.

So, take care if you go down the prop change as an easy fix - I doubt it will be.

With regard to lowering your transom and flooding going astern, yep, it's a pest. But it's the way to go IMHO. You could build a section for catching the water in front of the engine to prevent it coming aboard, I'm sure you will have seen such arrangements. Or even a dummy transom so only the rear of the boat gets a flood and it then drains out of the trunks. A bit of creativity will produce a solution I'm sure.

It's all a compromise. Good luck with it.

I agree with most of what Jeff says (kind of lost me when talking about Teddies ears ) and have quoted him with what I agree with.

If I were in your remote location and was confident the prop I had wasn't terribly off pare, I would be tempted to make set-up changes to change the handling characteristics without major outlay. Fair enough, changing transom height might not be your idea of fun. But it would be fairly cheap to do, wouldn't be overly difficult for someone with basic DIY skills, give you flexibility over set-up in the future and you wouldn't be disappointed if you'd bought an expensive prop only to find you weren't happy with it.

If it helps you, I'll measure the height between the planing pad and underneath of the outboard saddle on mine tomorrow. That way you can compare your outboard height with mine (sounds like I'll show you mine if you show me yours ).