Another hydrofoil question.

[Salty Canuck]

I know this has no doubt been asked before but here it goes again.

I have an 89 115 2 stroke on a 16.5 " Thundercraft bow rider.
Great engine with lots of power but finding it a challenge getting quickly up on plane.
I'm a newbe boater and have the ability with this engine to control the trim but little experience in doing so.
I believe to come up from start it best to have trim in neutral position or engine straight down and pour on the gas.
Comments as to my approach please.

I have been considering adding a hydrofoil as an inexpensive way of assisting in my quickly being on plane.
Can it be added to this engine and recommendations please.

Thanks

[DennisG01]

To get up on plane quickly, ALWAYS start with the engine trimmed "in" as far as it will go. In other words, trim it with the "down" button till you reach the bottom limit. This will also save fuel in the long run.

A hydrofoil could likely help, as well, but you really don't know 100% till you try it. They can also, sometimes, cause running problems. Meaning, you might have ventilation at higher speeds or during turns.

Another option (if you end up needing it) is installing Smart Tabs - google them - they are FANTASTIC.

Re-propping is still another option - but it would be best to know your current WOT RPM with a light load before doing something with a prop... or, really, that should be known before you do ANYTHING.

Still another thing you can do is to put an extra person (if there's room) in the bow when you're doing watersports. The extra weight in the bow will help quite a lot - especially on a smaller boat.

[zenoahphobic]

To get up on plane quickly, ALWAYS start with the engine trimmed "in" as far as it will go. In other words, trim it with the "down" button till you reach the bottom limit. This will also save fuel in the long run.

This not necessarily so, unless you are speaking with knowledge about the setup of the boat in question.
Quite to the contrary, generally trimmed in stops the bow rising, and as a consequence the boat is pushed more through the water slowing it's up to planning time and thus consuming more fuel.

You would start by having the engine trimmed perpendicular with the surface of the water; then experiment with gradual changes in or out trim.

[Salty Canuck]

Hydrofoil

Thanks to both senior members for taking the time to reply and will experiment before adding any accessories.
Will take a look a the tabs as often hear positive statements on those.

[DennisG01]

This not necessarily so, unless you are speaking with knowledge about the setup of the boat in question.
Quite to the contrary, generally trimmed in stops the bow rising, and as a consequence the boat is pushed more through the water slowing it's up to planning time and thus consuming more fuel.

You would start by having the engine trimmed perpendicular with the surface of the water; then experiment with gradual changes in or out trim.

Yes, the trimming in will help to stop the bow from rising. BUT, that's exactly what is needed for him to get up on plane faster. If the motor isn't down/in then the bow will rise up further and take longer to get on plane. Now, typically, you wouldn't want to run with the engine trimmed in all the way once on plane as it could push too much boat into the water and cause slow speed (and possibly listing).

So, what you do is: Start with it trimmed all the down, smoothly advance the throttle (full, if needed). As the boat "gets over the hump" and onto plane, smoothly back off the throttle and (at the same time) trim the engine up a bit. You won't want to trim too far up when you're pulling tubes or a skier (on two skis, anyways) because the speeds you will be using would be too slow to support planing AND pulling weight. You'd end up falling off plane.

The worst thing about all this... You have to get out there and go boating more!

[Salty Canuck]

Another hydrofoil question.

Thanks and if I must that is what I will do .... boat more!!

[Jason2tpa]

With a 115 on a relatively small boat you should have no issues getting on plane within seconds of throttling up. Unless you have an extraordinate amount of weight located in the rear of boat. Yes, a hydrofoil can help but with your engine's power you wouldn't notice a difference. While on trailer check to make sure the engine is able to trim all the way down and the height of the AV plate is no higher than bottom of hull or 1" below.

[DennisG01]

One other thing to consider, and hopefully this isn't the case, is that the engine is down on power... fuel supply, compression, etc.

[Salty Canuck]

One more hydrofoil question

Thanks to all really appreciate the help one can get from folks on this site.
My F115 has just been checked over by a marine mechanic and reported 130 compression on all cylinders.
I did not ask about the location of the engine on the transom as I hear of raising and lowering the engine to correct unwanted behavior.
The boat however has been run for years by a former owner so I assume if this had been an issue it would have been corrected. He was a mechanic.

I think the problem is the nut behind the controls.
The last run out was a slow start as in a river location and trying to keep the wake down.
I immediately started playing with the trim and probably had in a poor position to get up on plane as I reached a location to add acceleration.
On coming back in we had been at slow speeds as there was a lot of chop on the bay and our boat is only 16 plus a bit in length.
Again I had no doubt played with ignorance the trim in the chop so when closer to the harbor accelerated and when passing the 3k RPM motor raced but decelerated.
It seems to me having read input on this post I have been the problem with the use of trim and no doubt over use more the term.

In the future I will keep off the trim, tilt the motor straight down and accelerate up un plane.
Any use of the trim will be minor in very minimal increments and hopefully find plane easier and avoid cavitation when throttling.

Not a very short post for which I apologize and hope for critique of my summation from those, which is the vast majority, that know better than me.

[DennisG01]

No worries! VERY generally speaking, with the motor trimmed down it gives you better "grip", like having wider tires on a car because it puts more boat in contact with the water (in increases acceleration because it limits bow rise). With the motor trimmed up (as high as it can go before speed no longer increases or ventilation starts) you will get the most speed.

Just some more info... The motor racing certainly could have been because it was trimmed too high and started to "ventilate"... in other words, it started to suck air. However, it could also be a prop hub that is worn (we commonly refer to it is a "spun hub"). You would notice this, especially, when you're putting a good load on the engine - trying to accelerate fast or getting the RPM's up to go fast.

FYI, when you're trimmed down all the way, the motor will actually be tilted with the prop facing down a bit. This helps to lift the stern. Remember this from 6th grade Physics? -- "Every action has an equal and opposite reaction". Because of that, when the stern is lifted the bow is lowered. See that! Boating is actually based on science!

[cpostis]

To get up on plane quickly, ALWAYS start with the engine trimmed "in" as far as it will go. In other words, trim it with the "down" button till you reach the bottom limit. This will also save fuel in the long run.

A hydrofoil could likely help, as well, but you really don't know 100% till you try it. They can also, sometimes, cause running problems. Meaning, you might have ventilation at higher speeds or during turns.

Another option (if you end up needing it) is installing Smart Tabs - google them - they are FANTASTIC.

Re-propping is still another option - but it would be best to know your current WOT RPM with a light load before doing something with a prop... or, really, that should be known before you do ANYTHING.

Still another thing you can do is to put an extra person (if there's room) in the bow when you're doing watersports. The extra weight in the bow will help quite a lot - especially on a smaller boat.

Here's a couple of links for info on smart tabs, probably ideal for your small boat.
https://www.youtube.com/watch?v=sbOInDmFIVE

https://www.youtube.com/watch?v=0NmkN2SbA0w

I have Bennett hydraulic tabs and never trim motor down past level.

[Salty Canuck]

Another Hydrofoil question

Thanks for that and the tabs look to be the ultimate.
Is it thought to be overkill for a 16.5 foot bowrider?

[DennisG01]

Thanks for that and the tabs look to be the ultimate.
Is it thought to be overkill for a 16.5 foot bowrider?

Absolutely not. In addition to better performance "out of the hole", they will give you a more comfortable ride as it's gets a little choppy. They will keep the bow from bouncing around so much. One of the best bang-for-the-bucks you can do.

BUT, don't do anything until you get a little more time under your belt and have a better feel for it. You may find that you're happy with the way it is.

[pstephens46]

What do you do with smart tabs when riding downwind, following sea? I adjust mine up from helm. Do you stop boat and manually lift them?

[DennisG01]

What do you do with smart tabs when riding downwind, following sea? I adjust mine up from helm. Do you stop boat and manually lift them?

You could do that if the situation required it. But the Smart Tabs aren't as "firm" as regular, hydraulic tabs. Meaning, while they would still push the bow down somewhat, they're not going to have as dramatic of an effect as hyd tabs as they will flex up on their own with increased pressure.

The aspect of this, and this is only an educated guess based on what the OP has posted, is how he is using the boat... Sounds like it's primarily being used as a "fun" boat to run around doing skiing and tubing stuff. Now, I don't know the body of water he's in, but I'm going to make another guess that he's not going to be going out if it's rough.

I've also run a few boats with Smart Tabs (many more with real tabs) and I can tell you that it doesn't pose the risk you've (correctly) asked about of stuffing the bow - at least not anywhere near to extent that real tabs do.