Tiny tinnie prop options. Tell me I'm dreamin'?

[PeterKroll]

I've just been reading some old and new threads on prop options for larger boats, and really enjoying the comments. It's something I've never looked at, although all my boats have been tinnies around 14 foot or less (4.2m and down).

My current boat is a 3.9 Stacer Seasprite (sn AUAAJ000349QTX), no idea what year, but pretty old.

Outboard is a 2000 Honda BF25A 25hp 4-stroke, no tilt and trim, so it's a bugger to lift (as it is very heavy, over 70kgs), but at least it has electric start.

The Honda drives the boat really well, gets up to 30kph, gets on the plane very easily, uses bugger all fuel, trolls all day.

I know the horsepower is fine, and I've seen higher power outboards on similar boats, but I'm just wondering:

1) The outboard is very hard to lift, and I can't retrofit tilt and trim apart from the aftermarket ones, but I'm wondering if the motor is too heavy for the boat? Is 74kg on the back ok for a boat this size, safety-wise? (I did get some water over the back when anchored one day, but it seems like an unusual occurrence).


2) Could a different prop make any kind of noticeable difference to a boat this size, especially in fuel consumption (it already goes well and the truth is, I really don't want to go faster than 30kpm in this little boat).

[Gon Fishun]

Something for some of the more imaginative and deep thinking guys out there, what about a post 200-300mm long, attached vertically to the motor, no higher than the cowl, 1/2 inch diameter and keep a piece of hollow pipe 2 ft long in the boat to fit over it. So while your sitting at the tiller, slip the pipe over and gain extra leverage to tilt the motor. ??????

[PeterKroll]

Funny you should say that. I have a prototype for that from the bloke on the island who welded the step on my boat. So far it seems more trouble than it's worth, but it is a work in progress. I have seen some like that on other sites.

Further to that, I had someone give me an old Johnson tilt unit that the same guy says he might try to fit on there. I'm a bit iffy about adding even more weight.

Thanks for the suggestion. I'm interested in anything that might help with the weight of my beloved outboard.

[joey_1987]

I own a 395 Seasprite with a 30hp 2s Mariner. What diameter/pitch prop are you running? I was running an 11p x 9.5" diameter stock alloy prop which would give me 22-24 knots top speed, switched to a SOLAS 12p 10" diameter prop and I plane at lower speed, cruise at lower rpms (16-20 knots depending on load) and get WOT of 24-27 knots conditions/load dependent. 30km/h seems quite slow, do you know what rpm your motor is doing at WOT/is the speed gps confirmed? The boat can take the 74kg, but my 30hp 2s weighs 51kg so 23kg less weight. Nonetheless you should be doing 20+ knots not 16knots (30km/h) top speed.

[Chimo]

Hey Peterkroll

Have you considered podding your tinny? I did mine and no more water over the back even when backing up and you could even find they help tilting your motor. Cant help you with props. I just use what mine came with for general stuffing around and also as a pusher when moving stuff like pontoon and airberths etc.

http://www.ausfish.com.au/vforum/showthread.php?160166-Anyone-Ever-Podded-or-Podded-and-Trim-Tabbed-a-10-foot-Tinny&highlight=podded+tinny

Cheers
Chimo

[PeterKroll]

Joey, I am running a three-blade prop. The markings on it are 9-1/4X12 and 235X305. Not sure what they mean, but there is no brand that I can find. I got the 30km figure from the Navionics app on an Ipad 2. (I have also now discovered that there is a setting where I can change it to knots, so will do for the future).

This prop is the standard prop, according to the manual. I don't know what rpm it's running at for the 30km, but the manual says 5000-60000 rpm is max. It certainly doesn't feel as though it is working hard. Might be limited, I suppose.

The boat currently hops up on the plane very fast, but it doesn't seem anywhere near as fast as other boats with comparable 2-strokes.

[PeterKroll]

Chimo, I read that thread, and it certainly got my juices going. There is a bloke on the island who could fab that up for me now worries, but he would have to cut off the step that he welded on last week.

I couldn't tell from the photos, but did the pods follow the line of the floor? I could see that they are above the strakes, but they appear to be a little angled (might be an illusion from the tilt of the motor).

I have to say I love it.

[joey_1987]

30km/h is about 16 knots. Your prop is the stock alloy prop, 9 1/4 means it is 9 and 1/4 inches in diameter and 12 inches in pitch. Ideally WOT rpms shoud be known (I am about to buy a digital tachometer from China, search 'digital tachometer spark plug' on popular auction site starting with 'e', price is $11AUD ish delivered) which measures rpms by winding a wire around the spark plug. This would be useful as it would tell you if you are at the top or low end of rpms. Other things I would do if it was my boat was shift weight forward, mess around with trim holes to see which performs best in varying conditions. I found a Solas stainless prop for you: http://www.boats.net/parts/detail/props/H-58133-ZV7-012AH.html which is similar to what you have but 10" in diameter and still 12" in pitch. It should give you more speed, more acceleration and be more durable. Here's a link: http://www.boats.net/parts/detail/props/H-58133-ZV7-012AH.html you can also use the 'prop finder' to browse others-they have heaps on there. This is where I bought my SS prop from. Is your a short or long shaft boat? Long shaft shouldn't have water come over the transom, short may be an issue.

[Chimo]

Hi PK

did the pods follow the line of the floor?

More or less, and the side too. Check 9737097371973729737397374out the pics again. Works really well

C
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[PeterKroll]

Joey, thanks heaps for the info. I'm told that mine is a short shaft, but it looks to be sitting like every other outboard I've ever seen, with the prop in the normal place. The guy who told me this said that a long shaft will have an extension in the middle of the leg, and mine certainly doesn't have that. (I'll have a look at the serial number, which should tell me, I imagine).

I'm certainly going to get a new prop, like the one you recommended. Might see if I can pick one up second-hand, so long as it's pristine. I imagine that the real advantage of stainless would be that it doesn't flex under stress as much as alum. I'll research it.

If I understand, what you're saying is that the prop is pretty much the same as what I have, but s/s, and with larger blades at the same pitch. Have I understood?

[PeterKroll]

Chino, I never thought of this mod, and it's pretty exciting. Without doubt, the boat would sit better at rest.

When you plane, from the photos it looks as though the pods are acting as foils as well. Is this so, or are they out of the water? I was wondering, if they are out of the water, would they dig in and act as a brake when you do a tight turn?

I also noticed that you said that you had expert help. Is there any design to do with this, or is it just a couple of closed boxes sized to fit available space?

[PeterKroll]

Chino?.. My minds playing tricks again... Chimo... Ahh, not my failing mind, but my stupid auto spelling predictor. It made a much worse mistake this time, but I noticed and corrected it. :-)

[Chimo]

PK

The pods are not out the water so if they act like anything it would be like trim tabs fully up (much like my Vagabond Lencos when they are up ) with a bouyancy fringe benefit which is what I was after.

No digging in or braking on turns and yes the boat sits better at rest. I can stand on either or both so they support a GOM easily.

I told the expert what I wanted and he / his guys welded them up and welded them to the stern where they still sit. Basically closed boxes except I put bungs in just in case but I need not have bothered as the guys make fuel tanks!

C
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[PeterKroll]

Chimo, I'm pretty sure that this is going to happen, I see many advantages for my tinnie.

Did you rig the splash deflectors so the cowling wouldn't get so soaked? (Couldn't see anything in pics).

[joey_1987]

Yeah a new prop would be the go. SS props don't come cheap though even second hand, which is why I imported one. The prop I showed you costs $49.99USD to ship via USPS priority international (extra $12USD for express mail) which would bring the total to under $200AUD landed. If you find a good second hand one, by all means. Yes stainless props don't flex under load, they're heavier but thinner blades (less resistance through the water) and the one I mentioned is exactly as you said-same pitch and larger diameter, so it will push more water. If you knew your rpm you could mess around with pitch. Stainless is less forgiving if you hit something solid too-they will tend to break everything around them (gearbox etc) rather than an alloy prop which will sacrifice itself more on impact. The pods look interesting too, extra buoyancy and greater planing surface can only be a good thing in your situation. Also the motor serial number should tell you if it's a short or long shaft, also the degree to which the transom is 'cut' where the motor is mounted is quite a giveaway on this boat, my longshaft isn't really 'cut' much below the surrounding gunwale height.

[Chimo]

PK

splash deflectors so the cowling wouldn't get so soaked?

Good question! I foolishly fitted the bungs on the inside edge of the pods and the net result was that at high planning speed there was a lot of spray created.

I fixed the spray issue by cutting the tabs / finger handles off the bungs so solved the spray issue but when the pics were taken I had not done so.

Solution is to either not fit bungs or if you do fit them on the rear of the pod which is what I should have done, or not at all if the welder is good. I only fitted the bungs where I did to protect them on the occasions that the tinny was stood up on its bum for when it was to be carried upside down on the GQ roof racks.

Cheers
Chimo

[PeterKroll]

Joey, I have finally got the details of my outboard and it is a long shaft, according to the Honda distributors. The anti-ventilation plate is about level with the bottom of the keel, which may not be optimal, at least from what I have read. The bloke there was saying that the anti-vent plate should be 1 to 1.5 inches about the lowest part of the floor.

[davo]

I was under the impression that the stock props on the older Honda's were not very good. A relative in Townsville has a 40HP Honda and he changed to a Solas with excellent results. The whole 16 knots thing is strange. My 396 Clark Magnum 25 HP 2 stroke Yammy does 47Km/H with a bowmount on the front. My fathers 4.2 M TABS with a 4 stroke 30HP Yammy does about 23 Knots.

[PeterKroll]

Davo, I've been so happy just to finally have a little boat that none of these things have mattered. So now I've had it for a while, and I love having it, but it seems that I can't help tweaking it. I'm a big bloke, and it's a bit unstable and handles chop and boat wakes badly, so there are reasons..

Now I don't expect much from a tiny beast, but I really just want to have it running optimally. So current plans are pods and a new prop. But now I wonder if the motor is sitting too low? So I guess I need to look at that first. This is getting complicated!! :o

[PeterKroll]

By the way, I got the speed from the GPS on my Ipad. According to everything I've just read, it should be reasonably accurate. However, I have the Navionics app on the Ipad and also on my Nexus 4 phone. So I'll do a comparison next time I'm on the water. Could be tomorrow hopefully.

[PeterKroll]

By the way, Joey, I have ordered the rpm meter from China. We'll see how it goes.

[PeterKroll]

Chimo. do you remember offhand what thickness of plate was used? I saw some pretty thin aluminium toolboxes in Bunnings (the little brothers of the kind that go in the back of utes. I thought one of those chopped in half might do the trick).

[joey_1987]

Yeah I only ordered the rpm meter on Wednesday so shall see how mine goes too. When you get it and know WOT rpm's report back/compare them to your recommended max rpm's.

[PeterKroll]

Yes, I have the Clymer manual which gives me all that stuff. Pity I don't understand more of it.

[Chimo]

PK

I don't know what he used but the tool box is probably only 1.6mm and the issue will be the welding of that thin a material unless your welder is brilliant.

However I have just used some 1.6 checker plate which I think is the same as the tool boxes and its way too thin to walk on.

My pods are fine to stand on which makes me think that they were made from much thicker, stiffer material, maybe 3 or 4 mm.

Compared with the cost of getting pods built to suit the boat transom and follow the plane of the bottom to give you the benefit of bouyancy and tabs and or a longer boat I doubt I would skimp on the aluminium plate. If you have a good welder you probably should not put bungs in it either if you reckon the pod is watertight. You can always add them later if they are needed.

Cheers
Chimo

[PeterKroll]

Good advice, Chimo, thanks.