Exceeding max HP: 40 HP 2-stroke on a Mercury 430 Heavy Duty?

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dbachelor

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I just bought a new Mercury 430 Heavy Duty (PVC), for which the maximum power as stated on the hull is 30 HP (189 lbs, I believe). I am running a Mercury 20 right now, but looking at adding quite a bit of gear (a rail system to hold 4 seats and scuba or camping gear, etc). I haven't yet loaded it up with 4 divers and gear to test, but I anticipate having problems with the 20. Does anybody have experience to know how much I can push with 20 hp behind a 14 foot boat?

Assuming I find 20 HP to be insufficient, will 30 hp fulfill my wildest dreams, or will I wish I'd gone for more as long as I'm swapping out anyway? Would 40 hp be possible on this boat? I believe I can find a range of 2-stroke options under the ~190 lb weight limit, but I'd hate to rip the transom off with the power. I AM envious of forum users (@nobrainsd) who are pulling wake boarders with a similar boat and a 40, but I think the zodiac is rated for that power.

BTW, thanks for all the collective knowledge shared on here; this is my first post, but I have been reading for a while.
 

Sea Rider

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Re: Exceeding max HP: 40 HP 2-stroke on a Mercury 430 Heavy Duty?

Asume you are inquiring about a sib not a rib, right ? If so, will depend on how heavy duty your alum floor boards are, if overpowering, transom alum pannel board will act as a hinge specially when sibbing with tubes not inflated to it's recommended 3.5 psi factory working pressure. On the short run, will end bending or tearing both lateral side rails located at extreme of transom floorboard and sometimes alum lateral side joiners as well.

Nobrainsd has done some alum floor reinforcements on that sib and Zodiac is rated for that engine and probably has better alum pannels than Mercury. You can push your boat heavily loaded with 20 HP, but won't or have trouble trying to plane. Definitely a 30 HP has better punch than any 20 HP engine. Heavy duty stands for thicker PVC or Hypalon fabric, probably standard and heavy duty sibs shares same standard floor ?

Happy Boating
 

dbachelor

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Re: Exceeding max HP: 40 HP 2-stroke on a Mercury 430 Heavy Duty?

I'm not too sure about the floor; I bought it a couple weeks ago assembled, and I have yet to take it apart and examine the floor sections more closely. From what I can tell, it seems pretty stout and looks similar to the cross section shot of Nobranisd's Zodiac floor panels. I am planning to bolt a system into the floor with three uprights down each side and a rail about 12" high that runs the length; I will mount seats on these as well as securing gear. Your point about the transom/floorboard juncture acting as a hinge makes me think I should extend the rails all the way back and into the transom; that way, the motor will effectively be pushing the people and cargo more direcly as well as the boat (instead of just pushing on the floor and tubes). This would also reduce or eliminate that hinge effect, and might help me get away with the bigger motor. I will post some pictures once I get this going, hopefully over the weekend.
 

Sea Rider

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Re: Exceeding max HP: 40 HP 2-stroke on a Mercury 430 Heavy Duty?

Yes, definitely, extending the rail all the way to the transom alum pannel ending + maybe extending into the transom itself will be the way to go, being Mercury a Asian manufacture you will only find 2 floor pannel market available, the one with tiny spaghetti like form close to each other and the stripe type pannel, check pic. The second type is much better.

On the markey you can find metal frames that are placed on top tubes to place/bolt seats on the formed structure, that way won't need to use the floor to place seats. Will have more interior space for diving gear.

Happy Boating
 

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riverandocean

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Re: Exceeding max HP: 40 HP 2-stroke on a Mercury 430 Heavy Duty?

I used a Bombard 14' with a 20hp Honda for a number of years..... I frequently loaded it with 2 adults 2 kids and camping and fishing gear and food for 1 or 2 weeks and set off.....

after awhile the plastic boots that hold the transom to the tubes started to tear....... big problem...... not an easy repair.

Now I run a 30hp Honda on a 14' Grand Raid which is a heavy duty hypalon Zodiac from their milpro line...... very robust boat... rated for 50hp..... fully loaded (all the gear I mentioned above) I can easily plane. The 30 hp motor has a lot more grunt power..... I contemplated buying a 50hp motor but the weight of a 50hp four stroke put me off, even thought the boat is rated for that weight and power.

The engine ratings I would think are there for a reason..... how robust the boat design and manufacture is......

If you push the rating you definitely risk some repair bills!

R&O
 

paulpost

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Re: Exceeding max HP: 40 HP 2-stroke on a Mercury 430 Heavy Duty?

20 or 40 HP in the 2 strokes area from the same manufacturer like mercury or Johnson are the same engines just bigger carburetors and compression levels so do not go over the wight limit that is posted on the label,
If you are concern about the transom and you have to be do not run wide open but just when is necessary and do not forget the limits that the manufacturer is posting are the one they are comfortable with and keeps them in the safe zone (out of lawsuits)
 

Sea Rider

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Re: Exceeding max HP: 40 HP 2-stroke on a Mercury 430 Heavy Duty?

There's a big difference in HP and weight between a 20 and a 40, most brands will jump the 20 HP in 2 strokes, so will have 15 to 18 HP in the near 20 HP range, next are 25/30 same weight and a 40 is another story. You can place a bigger engine on transom than recommended, but for light boating use, if in heavy use, heavily loaded and going commercial the extra torque and weight will do the hinge effect bending side rails & side joiners on transom floorboard.

Usually slat floorboards sibs are rated for less HP than non slated one piece alum floorboardsl sibs, so stay in the max engine recommended for that sib.

Happy Boating
 

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dbachelor

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Re: Exceeding max HP: 40 HP 2-stroke on a Mercury 430 Heavy Duty?

R&O, thanks for chiming in. Could you tell me where the rubber boots started to tear? Inside/outside, top/bottom? I am designing a rail system which will hold the seats and cargo and tie into the transom, which should relieve a lot of the stress from the transom/tubes joint... I have been trying to figure out where the 1st point of failure is most likely to be (I am thinking that the top of the transom might start to pull backwards due to the torque of the motor "pivoting" on the bottom of the transom).

The weight limit on the transom for the motor is 189 lbs. The Nissan/Tohatsu 40 (not TLDI) weights ~130 lbs (not much more than my current 2-stroke Mercury!), so I'm not too concerned about the weight itself; much more so the extra torque. As the boat is rated for near 2000 lbs of gear and people, I do not think that 40 hp is a ridiculous amount of power to put on it. I put 4 people in last weekend and could plane with my Merc 20, but only at mostly full throttle. Add any diving/camping gear, and forget it. So, I am still considering the upgrade and suspecting that I could get away with it, however the "hot deal" on a 2004 Tohatsu seems to have gone a bit cold. I will be bolting bases into the floor and piecing together my rail system over the weekend, so I will post some pictures of the floor sections and my rail system.

That hinged floor section is pretty ugly--I hope to never see that again!! So if I'm looking at this correctly, that bent downwards, is that correct?

Thanks again for the thoughts, everybody.
 

Sea Rider

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Re: Exceeding max HP: 40 HP 2-stroke on a Mercury 430 Heavy Duty?

By rubber boots are you reffering to both triangular lateral rubber inserts, they simply came off, a matter of re gluing with appropriate heavy duty glue, yes transom alum floorboard tends to bend downwards when excesive & long time overpowering. The problem with this type of alum pannel floor is that it's compossed of several slats secured side to each other by internal rails which naturally bends sideways, are kept in place to riveted lateral alum rails.

If you look closely the lateral rail has a long tear towards transom side even though the sib is permanent infated to 3.5 psi. In this case, the real stress floor isuue comes from placing a 30 HP engine on a sib rated for max 20 HP engine. If naughty owner want's more power than factory recommended is at it's sole risk, anyway aware of some boaters madness :rolleyes: have in stock all spare parts to repair those floors.

Happy Boating
 

TOHATSU GURU

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Re: Exceeding max HP: 40 HP 2-stroke on a Mercury 430 Heavy Duty?

R&O, thanks for chiming in. Could you tell me where the rubber boots started to tear? Inside/outside, top/bottom? I am designing a rail system which will hold the seats and cargo and tie into the transom, which should relieve a lot of the stress from the transom/tubes joint... I have been trying to figure out where the 1st point of failure is most likely to be (I am thinking that the top of the transom might start to pull backwards due to the torque of the motor "pivoting" on the bottom of the transom).

The weight limit on the transom for the motor is 189 lbs. The Nissan/Tohatsu 40 (not TLDI) weights ~130 lbs (not much more than my current 2-stroke Mercury!), so I'm not too concerned about the weight itself; much more so the extra torque. As the boat is rated for near 2000 lbs of gear and people, I do not think that 40 hp is a ridiculous amount of power to put on it. I put 4 people in last weekend and could plane with my Merc 20, but only at mostly full throttle. Add any diving/camping gear, and forget it. So, I am still considering the upgrade and suspecting that I could get away with it, however the "hot deal" on a 2004 Tohatsu seems to have gone a bit cold. I will be bolting bases into the floor and piecing together my rail system over the weekend, so I will post some pictures of the floor sections and my rail system.

That hinged floor section is pretty ugly--I hope to never see that again!! So if I'm looking at this correctly, that bent downwards, is that correct?

Thanks again for the thoughts, everybody.


Don't over power:

No insurance

Automatic liability for any accident

No warranty

Depending on your state...Illegal

Stress on the boat
 

nobrainsd

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Re: Exceeding max HP: 40 HP 2-stroke on a Mercury 430 Heavy Duty?

Well, I am not over powering my zodiac and I am not familiar with the actual construction of the mercury floorboard, but I do have a couple of comments.

The transom to tube connection is always going to be under stress and is a common point of failure, but it is designed to take the loading as your you outboard weights and unweights up and down. The amount of stress from some extra thrust is nothing compared to this dynamic loading. I don't recommend exceeding the rated HP, but it is the transom weight that is the real limit. Just consider what the forces must be when your outboard and boat go airborne then slam into the sea.

The aluminum floor design is very strong when all of the component pieces fit well and the boat tubes are fully inflated, but I would not try to make the floor to transom a fixed connection. You aren't going to be able to easily create floor to transom connections that can withstand the stress. The flexibility of the system is key to it's design. The floor can give and move at the transom joint. That is a good thing! I have not reinforced the side stringers nor the aluminum panels in my floor to deal with these kinds of stresses. My reinforcements are at the attachment points for my seating, the cross plates I have that my battery and gas tank bolt to and the cross plate that my ski pole mounts on. One of the things you don't want to do is create isolated stress points in the aluminum floor top sheet. Aluminum is strong for it's weight but it flexes and cracks rather easily. Avoid holes or any kind of mounting point that isn't backed up to spread the stress. It is also important to remember that any large load needs to be spread out. Watch to avoid having the load distributed by volume rather than weight! That isn't always easy or convenient, but the floor can handle a lot more weight that isn't all in one place.

Really secure your gear if the ride is rough or you are working through large swells! The aluminum floor is very strong, but does not take dynamic loading well unless it is dispersed. Dents, holes and other damage to the top sheet on the floor significantly decrease the strength of the hollow floor panels. Idon't doubt that it is possible to fold a floor section when loading up, but that is much more likely if something like tanks are bunched together and aren't held tightly to floor. Even relatively light stuff will apply considerable force when accelarated up and down independently of the floor itself.

Obviously, I think that while more thrust may take you faster and lead to more dynamic loading (gotta launch!) the thrust itself is not generating the largest stresses on the boat. But what do I know :)
 

dbachelor

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Re: Exceeding max HP: 40 HP 2-stroke on a Mercury 430 Heavy Duty?

SeaRider, R&O had mentioned the "plastic boots" separating between the transom and the tubes; I do not think he was talking about the rubber triangles (which on my boat are slack and do not appear to be structural). I did not get as far this weekend as I was anticipating, but I did get the floorboards out to install a couple of the bases, and I see what you are talking about--my floor boards come out in three large sections, each of which consists of several pieces riveted together into side rails. Left as-is, I could imagine the torque eventually tearing the bottom of the rail out, just as in the picture you attached. Kind of makes me tempted to weld a length of aluminum angle down each side of that rear floor section, and attach THAT into the transom... might be getting carried away, though.

I am attaching a couple pictures of what I have underway; I am building a frame out of Speedrail with bases bolted into the floor in 6 locations (in the middle of each floorboard); it will bolt straight into a vertical section of 1/2" angle on the transom, as well as a diagonal that will go from the transom down into the 1st base. The PVC pipe in the pictures was only for modeling; I have a shipment of 1 1/2" anodized aluminum Schedule 40 coming today which should be plenty stout. This does take up some deck space, but I just didn't feel great about setting a bunch of weight on top of points along the tubes... this will make use of the available space much more efficiently, as well as adding a 2nd layer of structure to the hull.

If anybody is counting, the floor is just about 15/16" thick, with the layers of aluminum being about 1/10th.




IMG_20110605_182959.jpgIMG_20110604_173230.jpg
 

Sea Rider

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Re: Exceeding max HP: 40 HP 2-stroke on a Mercury 430 Heavy Duty?

A language confussion, transom holders were reffered to as plastic boots. The alum floor pic example shown is 12.5 mm thick. If the under rails would be slight thicker, would support more stress punishment. The issue about bending transom floors and side rails on a standard sib is done mostly by :

1-Exceeding max engine for that inflatable boat application
2-Having inflatable heavily loaded and poorly inflated to it's factory working pressure
3-Using a recreational inflatable for heavy workboat use
4-Constant idle/wotting use & stress under points 1, 2, 3

Other than that, well inflated, correct inside weight distributed and max engine permited will give a "long live the sib"

Happy Boating
 

dbachelor

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Re: Exceeding max HP: 40 HP 2-stroke on a Mercury 430 Heavy Duty?

A bit late, but as promised: here are some pictures of the modifications I did to the boat. I started with a box of 1-1/4" speedrail fittings I found used, bought 60 ft of anodized 6061 pipe, and went at it. The bases are bolted in through 1/4" aluminum backings inside the floor sections, and the rear of the frame is tied into the transom via 1/2" 6061 angle.

With this setup, the rear seats and helm can be positioned and then clamped down for comfort and weight distribution to accommodate different loads; and there is a matching front pair of seats which drops onto the rails with modular fittings. I figure I can also put a crossbar on to secure camping gear, or a rack for scuba tanks etc.

The helm and controls are the simplest/cheapest solution I could come up with--as you can see, I opted to simply continue using the tiller handle for throttle control (which I extended with brake cables for a tandem bicycle); a little hokey, but I plan on changing out the motor to a 40 with controls when I find a good deal. I also need to build a protective box on the back of the helm; might have a friend weld up a stainless box.

There is still room for flex, but the juncture at the transom is very stout... and the motor is well tied into the boat's load instead of just the tubes and rear floorboard, so I feel fairly confident powering up now.
 

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Sea Rider

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Re: Exceeding max HP: 40 HP 2-stroke on a Mercury 430 Heavy Duty?

Nice floor & transom reinforcements, congrats, lot's of skilled work involved; Don't forget to inflate sib to it's factory recommended working pressure with a gauge if wanting tube rigidity to work well with new transom reinforcements.

Long time wanted to go for the non plus ultra floor update, have placed (2) long one piece side joiners with fabric ends reinforcements on all new large 380-420-460 sibs instead of the standard 4 pieces (2 short, 2 long) factory delivered. Panel floor now has much more front & side rigidity when tubes are well inflated, has eliminated forever the hinge effect experienced on badly inflated sibs's tubes with standard 4 pieces side joiners when using as work boats. Long Live the Sib.

Happy Boating
 

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Pack Rat

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Re: Exceeding max HP: 40 HP 2-stroke on a Mercury 430 Heavy Duty?

Hey Sea Rider ...thanks for that tip about flipping the long/short side joiners so they are not twins to the other side. Noticed it was much stiffer and quieter right away.
 

dbachelor

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Re: Exceeding max HP: 40 HP 2-stroke on a Mercury 430 Heavy Duty?

Don't forget to inflate sib to it's factory recommended working pressure with a gauge if wanting tube rigidity to work well with new transom reinforcements.

That's a good point; I have historically left the pressure a little low (so I don't need to worry about over inflation), so I have been trying to pay more attention to the pressure gauge lately. I have been increasingly concerned about expansion from heat after noticing it and reading through some threads... I sure wish I had the piece of mind that would come with pressure relief valves. Does anybody know if pressure relief valves are an aftermarket option (The Merc has Halkey-Roberts valves)? Even sitting in the water, with the afternoon sun coming out from behind the clouds for a while, I noticed an increase of nearly .5 PSI... It's not a big deal to unscrew the cap and let some pressure off, but it WOULD be a big deal to forget once at the wrong time!
 

dbachelor

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Re: Exceeding max HP: 40 HP 2-stroke on a Mercury 430 Heavy Duty?

Pack Rat, your picture makes me anxious to take my boat out diving! Looks fantastic... unfortunately, we have no clear water here in the NorthWest...
 

Sea Rider

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Re: Exceeding max HP: 40 HP 2-stroke on a Mercury 430 Heavy Duty?

Hey Sea Rider ...thanks for that tip about flipping the long/short side joiners so they are not twins to the other side. Noticed it was much stiffer and quieter right away.

Pack Rat, you are welcome, as you see have done strenuous experimentation to better the overall ride of sibs & ribs once on water, apart from adding whatever accesory you would like to count onboard, seems have reached the tech limit regarding new cracy experimentation which really love. Yes, twin joiners same lenght placed in front of each other will give hinge effect specially when tubes are underinflated riding in rough waters, jumping waves, using sibs as workboats, will end bending or breaking side rails that secures alum slats that forms each panel against them. If possible change for 2 one piece long same lenght side joiners. Will experiment better sea ride under all water conditions.

Dbachelor, didn't get clear if you currently use a pressure gauge, fingering tube is the most non accurate method for checking tube's overall pressure and you have generally 3-4 chambers to inflate evenly. Since my boating beginning have always used gauges, not a single problem with unpleasent ride, unglued transoms, bending, breaking side rails, etc. A tip, call Defender and check if they have a spare hose & gauge that comes standard with Bravo 4 Kite, will need to buy spare yellow bayonet type end plug as this model seems to come with multiple push type fittings that will not match HR valves. A must have issue. Sorry Zodiac, Avon !!

Pressure relief valves are only found on larger and more expensive boats unless you buy and install them apart, don't use them as already know our local all year round summer/winter air/water temperature so to play a bit with different inflating pressures before boat is launched to sea. A slight over inflation on boats that have seams in good working condition will not be a issue to worry about, you'll be surprised at the pressure each boats is tested at the factory for 48 hours before being delivered to dealers.

Happy Boating
 

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dbachelor

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Re: Exceeding max HP: 40 HP 2-stroke on a Mercury 430 Heavy Duty?

Pressure relief valves are only found on larger and more expensive boats unless you buy and install them apart, don't use them as already know our local all year round summer/winter air/water temperature so to play a bit with different inflating pressures before boat is launched to sea. A slight over inflation on boats that have seams in good working condition will not be a issue to worry about, you'll be surprised at the pressure each boats is tested at the factory for 48 hours before being delivered to dealers.

Happy Boating

Hey Searider, I went back and found the quote I was remembering about aftermarket pressure release valves, and it was from you! This was back in May, in the thread "Inflatables blowing up from heat (air) expansion.":
"An Italian manufacturer has come with a pressure relief valve that screws on top Halkey Roberts Valve, you can attach a pump to side of system to inflate sib, once 3.3 psi is reached will open spring coil to release overinflation, works too while baoating under excesive sun."

This sounds like what I want; I had the boat out at 10pm this weekend, having topped it off in the cool air; now it is sitting at home outside with the afternoon sun. Did I remember to bleed air out before parking it at 1pm? no way! I just want to avoid this kind of stress-- on my mind and the boat! Plus, we often have cool days around here that might well stay cool all day OR heat up very quickly if the northwest fog burns off, it is hard to plan for consistency. So, If there is a screw-on solution for HR valves, I am extremely interested... I AM using a pressure valve, btw; and I hear what you're saying about slight overinflation not being too much of a concern. Nevetheless, there are enough stories on here about people having seams blow that it makes me concerned of the possibility of that happening while relaxing on a beach miles from home!
 
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