Calling Honwave T35AE owners with a 20hp

[flames7607]

Hi Everyone,

I have the Honwave T35 AE / BF20 package from Honda

What size/pitch props are you running ? I have a few issues (which I won't bore you with yet), and want to check if the previous owner (package is 2019) has changed to an unsuitable prop.

I know that there are a huge number of variables with prop pitch, RPM at WOT, loading etc. For now I just want to see if my prop is more or less standard.

The BF20 is running a 9-1/4 x 10 inch prop

Cheers

[Fenlander]

Actually explaining what your issues are is key to the forum advising on a prop dilemma.

In the 10" pitch you have the size most frequently fitted pitch as a standard prop for this motor.

A 20hp on the T35 with an average load should get on the plane easily and reach something in the 17-20kts region.

When I owned this model SIB with a 15hp I found it a little more prone to hanging for a few seconds in the transition to plane than other SIBs I've owned but a 20hp should negate that.

To check the prop is suitable for your needs you should fit a budget (£10) tach and see what revs you are getting at max throttle/speed compared to the rated revs of the BF20.

[flames7607]

Hi everyone,

Sorry for the delay, I've been gathering some real world data.

So, the issues

1. The boat gets up onto the plane with 2 adults, providing one of them is sitting on the front bench, this takes some 5-10 seconds. If they are behind the bench, by only a few inches, the boat won't go onto the plane, even with full throttle. Once on the plane, the front occupant can move back behind the bench with no adverse effect.
2. When on the plane, at least 3/4 of the hull is in the water, and the "release point" ie where the water and the hull meet, is close to the front of the boat. I have tried the engine in different positions (transom angle) by moving the pin, but this has no noticeable effect on the hull. I had expected the plane to be better with the pin further back.
3. There is no noticeable increase in speed of the boat between 2/3 throttle and WOT, that last third of twist is a dead zone. RPM at WOT is 5460 on a flat sea, 22 mph. Specs state RPM at WOT should be 5000-6000
4. The boat and the motor feel like they are bogging down.

For context, I owned a 16ft fishing boat for many years. I know a SIB is a totally different beast, but I was expecting it to plane further back and not bog down at open throttle. It doesn't feel like a fault with the engine, but more a prop / trim issue.

I welcome peoples thoughts.

Cheers

[Fenlander]

Your maximum speed is about what I'd expect but with issues getting on the plane and a feeling of bogging down if the motor otherwise is running well I might try a 9" pitch prop.

I assume you know your tube and keel pressures are OK even after that slight cooling when you put it in the water?

[flames7607]

Yep, tube pressures are good.

So lower pitch prop will increase RPM, you think that may address the dead zone and plane issue ?

It feels like the boat is encountering some sort of "barrier" ie not sitting on top of the plane fully.
Should I expect there to be less of the boat touching the water, or is this a characteristic of SIBs ?
It's strange that the motor/prop seems to lack the oomph to get onto the plane if the front passenger isn't sitting all the way forward.

[Wazzajnr]

Does the boat poke its nose high in the air when you wind the throttle open from low speeds?

Just wondering if your engine might be set a bit low?

Can you see the cav plate when on the plane?

[Max...]

If you’re hitting 5500 WOT then that’s not that far out and shouldn’t really explain fully such poor performance In getting on the plane. Two adults but what ‘size’ and what else are you carrying?

You’ve got a heavy boat and engine, every kilo counts with these SIBs in terms of power to weight.

Can you post up some pics of the engine installation?

[Limecc]

Sounds like a hole in the power curve and something's off. A lower pitch prop would help as you are currently over propped by 2 pitches.

[paddlers]

Can't help with what prop etc but my 3.5 AE would plane 5 adults with a 20 hp 4 stroke Tohatsu so something's definitely off with your outfit . It was very quick two up and I'm not skinny at 20 stone. Weight distribution forward also really helped to get it on the plane but once there you could move back with no detrimental effect whatsoever.

[flames7607]

So, I weigh 82kg, and sit on the rear right corner, my passenger weighs 100 kgs and sits on the left had side of the front bench. The only other weight at the moment is the fuel can.

Wazzrjnr, Yes, the nose rises up about 20 degrees when opening the throttle to get it on the plane, and then goes back down once on the plane ( when 2 people on the boat) If the passenger sits just behind the front bench, then the nose will rise even more, and the boat won’t plane, it just seems to wallow. I took it out on my own, with the only weight being me (82kgs) at the helm, and a full can of fuel(12 litres) halfway along the deck, and the nose rose to some 45 degrees (quite alarming) before going on the plane.
The cavitation plate ( the highest horizontal plate on the engine leg ?) Yep, I can see that when planning, it’s just (and I mean Just) below the water level when planning. It’s deeper under water when stationary.

Limecc – when you say “over propped by 2 pitches” do you know what the engine would have come with as mid range/standard prop ?

Paddlers – when on the plane on your 3.5AE, where was the point where the hull met the water ? Mine is just in from the nose, and certainly no more that quarter of the way back down the hull. I think this is dramatically affecting the handling. When out on my own, the rear of the boat "skidded" around a huge amount in turns, very very twitchy.

Thanks everyone for your responses so far. The only pic I have shows the transom with the outboard. More pics to follow

[Limecc]

Originally Posted by flames7607

Limecc – when you say “over propped by 2 pitches” do you know what the engine would have come with as mid range/standard prop ?

Sorry no. It doesn't matter what it came with as they will fit what they've got. If Fenlander says 10" is most common then he's probably spot-on. What matters is your real life tests which provides the needed info.

If your combo is 500rpm short and one pitch adds 200rpm then that puts you at 5900rpm and you'll not lose any top end but gain lots of holeshot (8" prop).

If you give the GPS speed then we can calculate prop slip to see if it's acceptable.

[Wazzajnr]

The cav plate is the big plate just above the prop.
If there is another plate higher up and that's in the water then the engine is too low on the transom.

[flames7607]

Pretty sure it's this plate I was describing.

Considering it's a package sold by Honda, I'm thinking the engine is correctly mounted on the transom. Any higher would look odd and I'm thinking would over stress the transom ? But I bow to other peoples knowledge on the subject.

[Limecc]

Originally Posted by flames7607

Pretty sure it's this plate I was describing.

Considering it's a package sold by Honda, I'm thinking the engine is correctly mounted on the transom. Any higher would look odd and I'm thinking would over stress the transom ? But I bow to other peoples knowledge on the subject.

Before considering a prop change the engine height must be correctly set. The motor needs to be as high as possible on the transom and the prop not ventilate.

That's not the AV plate that's a deflector plate.
Here's a helpful diagram from this thread:
lower unit vrs water flow

The Anti-Ventilation Plate and other Nomenclature

[flames7607]

That's a good article, will do some photos of the boat and engine, in and out of the water, and report back

[Wazzajnr]

Originally Posted by flames7607

Pretty sure it's this plate I was describing.

Considering it's a package sold by Honda, I'm thinking the engine is correctly mounted on the transom. Any higher would look odd and I'm thinking would over stress the transom ? But I bow to other peoples knowledge on the subject.Attachment 138191

Honda will sell many more engines than they will boat/engine packages so the engine will be a compromise of the majority of users.
The boats will probably not be made directly by Honda but bought in and branded as such (don't quote me on that, I may well be wrong)

Engine bring too low will put far more stress on the transom than too high.
Also your symptoms sound like you're getting on plane but have a lot of drag once there which again sounds like too much leg in the water.

Anyway, whatever the reason, it's totally possible for the engine to be sitting a bit low.
Imagine if the prop were 2 feet under the water and the transom is the fulcrum point, the boat would flip every time.
In a perfect world, you would want the thrust pushing the centre of the transom but we know that won't work as the prop is out of the water.
The higher the prop the better upto the point where it cavitates/ventilates.

I have similar issues with mine and am convinced that engine height is a big factor. I have also bought a doel fin to see if it helps.

My plan is to test current setup against raised motor against doel fin and report back.

[Wazzajnr]

By the way, ON the pic you posted from the manual, the part ringed in red isn't the cav plate so again looks too low.
As said before, pics of the back of the boat would help.

[Limecc]

Originally Posted by Wazzajnr

By the way, ON the pic you posted from the manual, the part ringed in red isn't the cav plate so again looks too low.
As said before, pics of the back of the boat would help.

Apologies for being pedantic, the av plate you refer is not a cav plate.

Originally Posted by Wazzajnr

My plan is to test current setup against raised motor against doel fin and report back.

The doel will function great as an oversized AV plate.
I realised I'm keeping my own fin so I'm going to raise the engine another hole I might not otherwise get away with.

[Wazzajnr]

Apology accepted and yes you are absolutely correct. However they are widely referred to as "cav plate" and that is shorter to write than most other versions and I'm pathologically lazy.
Pretty sure everyone knew what I meant. �� ��

[Fenlander]

Scattergun thoughts...

Flames your weight is about the same as mine but your crew a good few stones heavier than Mrs F who would sit on the forward seat. Then we'd often have one or two light teen girls around 45kg each as the moveable ballast.

As I said above I found the T35 the SIB with the highest bow rise and slowest transition onto the plane of all the SIBs we've owned. I know Paddlers experience is different but I can only report how it was for us. Of course we only had a 15hp but I would have thought that was offset compared to Paddler's 20hp as he could plane OK with 5 adults.

Yes you are right SIBs compare badly to many hard hull smallcraft in their plane transition and performance... it's just the offset for something that will fold up and go in the car.

Re prop pitch 10hp motors come with 8" or 8.5" props, sometimes but more rare a 9".... 15hp motors with a 9" or sometimes a 10"... 20hp with anything from 10"-12". Usually a 10" pitch on a 20hp is perfect unless the load is excessive and it's not in this case. So normally I'd not be guestimating anything less than a 10" for your outfit except you describe behaviour and rev readings that indicate pitching down might help. Don't go as low as an 8" though as the theoretical prop slip/pitch calcs don't work out well for SIBs and as I said above an 8" is the pitch for a motor half your HP.

However what might skew the above is if you have a 4 blade. They often perform as if a pitch 1" higher than a 3 blade. In theory they should get on the plane well with their greater grip but that grip comes at the expense of more drag. I prefer a 3 blade with swept design (like the OE on Mercury 2-strokes) on a SIB.

Unless a SIB is lightly loaded say one up they rarely plane in a perfect racing way with just the transom end in the water. The moment you load them up they tend to plane with most of the SIB in the water.

Having said that the skiddy/twitchy feeling you describe while somewhat a character of a SIB compared to a hard boat sounds like bow steer and could be a result of having the heavier person forward and the trim pin in the posn you show. It would be interesting for you to pull the pin back one or two holes and/or swap between you and crew and see what difference that makes when on the plane.

Re the AV plate height relative to the bottom of the transom... unless you have it drastically out by having a longshaft fitted the T35 doesn't seem that critical to an inch or so up or down on the ideal. It's mostly just drop the OB on and go.