Hp Rating For A 385 Explorer

[Lukeinsyd]

Howd'y,

I'm looking for some oppions on fitting a larger HP outboard to my modified 385 explorer? What are the known consequences apart from void insurance etc?

I'm currently running a Yamaha 2cly 25 CV which has been modified to a 30HP. In most circumstances (fishing, trolling etc) this combination works ok but I'm looking for more power to enable the occasional pull of a knee board and tube etc...

The Hull has a transom weight rating of 85kg the motor I have in mind is approx 74kg SS Tohatsu 3cly 50HP no tilt/lift or electric start. I don't think weight would be too much of an issue as the 50HP weighs only a little more than a 20HP Honda 4 stroke! Also, I don't think useing the 50HP combination when fishing would put too much extra stress on the transom (not looking to exceed the hulls ability in the available conditions) but what about the occasional tube pull etc..do you think the stress forces would be too much?

I have included a few photo's of extra's fitted to the boat which might help explain why currently 30HP is not enough...dual fuel tanks, batteries, floor and casting, bait tank, console etc...

Looking for oppions guys?

[a boat]

Hi Lukas, if the boat is insured than by putting a 50HP you will not be covered in an accident and I think the transom would not be strong enough to cope with the extra performance, the weight will not be a factor if the Tohatsu weighs what you say, but the thrust will damage a transom only designed for 25HP.

I would not do it myself, but your call.

Cheers,

Huey.

[Lukeinsyd]

Thanks for your reply Huey. The boats not insured and probably not worth it, but as you say if involved in an accident this is an issue which is worth considering. Have you seen damage caused by an overpowered transom before? do they crack or buckle & what are the weak points?

[pelican]

If it just kids for tubing just buy a ally prop of a lower pitch if your current one is labouring pulling them or keeping on the plane but you have to be careful not to over rev the motor. Worth trying just to see if they really enjoy it or if it's a fad. It's onlya few minutes to change back to your "fishing prop". Some tube designs need a heap less power than others to tow as well. Kids get a thrill at a low speed so you don't need much for them to have a good time. As for teenagers or adults doesn't matter what power you put on any boat it's never enough after a while as you always want more speed and you progress to faster ski boats.

As mentioned I wouldn't ever go above a boats rating as insurance company will crucify you and you can eventually kill the hull. Unlike in years gone by they are better engineered but only to the limits not overengineered like some older craft were. Also check your current policy as many have an exemption on towing toys or skiers and you need to add t as a extra.

With your "30hp"' update you might want to actually double check you are really getting the benefit not just sucking extra petrol. Many so called mechanics do the mods but it is really only suitable on some models and many remove restrictor plates , throttle stops or cut exhausts but neglect to change carby jets etc etc. These mods may seem good at the time (and some are) but a lot reduce the life of your motor unless done by someone who really does now what they are doing. Most don't and it may sound better etc but if your using the same prop and getting the same revs you may have gained little.

When you think about transoms think about how much difference a 10mm uncontrollable flex will make to your trim and think how deadly thet would be at speed if you got any prop aeration or started porpoising. It could be uncontrolable flip or submarine. That's without considering the fatigue metal and welds in the transom are enduring. HP / torque in boat motors is not linear in the way it is applied at the prop as a 30hp may be able to place twice the torque at particular revs compared to a 20hp upon acceleration. A 30 with larger prop could apply twice the torque in half the time and that is an extreme change in load on a transom not designed for it.

Edited November 28, 2007 by pelican

[squizzytaylor]

I have a friend who has put a 40hp etec on his 4.00 stacer (rated to 30hp) v-nose Lukas and the thing is an accident waiting to happen, as mentioned the transom is NOT strong enough and the boat is just not designed for it,(in answer to your question yes the transom is distorting) it its a lovely motor and I can vouch for the toey 3cyl motors personally but I would think twice before doing it, also have a think about the consequences if someone else were injured by the boat as you personally would be liable to prosecution if found at fault.

Just my opinion, by the way, cool looking boat.

GT

Edited November 28, 2007 by squizzytaylor

[a boat]

Thanks for your reply Huey. The boats not insured and probably not worth it, but as you say if involved in an accident this is an issue which is worth considering. Have you seen damage caused by an overpowered transom before? do they crack or buckle & what are the weak points?

Hi Mate, yes I have seen many boats of all brands with damaged transoms due to overpowering. As usual some good advise from Raiders and I think the boat will break with anything more than a 25HP.

Cheers,

Huey.

[Lukeinsyd]

Pelican: Thanks for your repsonse some very good information I hadn't yet considered. To be quiet honust I was a whisker away from buying the 50 and mounting it up & taking my chances but I'm glad I took the time to do this post... you guys have certainly swayed that decision! - In a good logical manner.

Squizzytaylor: Good to here other's experiences to reinforce the decision. Thumbs up mate

Huey: The decison is now made to remain "status quo". I'm getting that feeling a might have been asking more from the boat than what is capable...might be time for an upgrade

Can anybody reccommend a good outboard mechanic to verify the modifications on the Northern Beachs Mona Vale & beyond?

Any oppions on what she might be worth $ ?

[bate_Bay_fisho]

i agree, 30hp is good, you woul not what it any bigger then that

[pelican]

Pelican: Thanks for your repsonse some very good information I hadn't yet considered. To be quiet honust I was a whisker away from buying the 50 and mounting it up & taking my chances but I'm glad I took the time to do this post... you guys have certainly swayed that decision! - In a good logical manner.

Squizzytaylor: Good to here other's experiences to reinforce the decision. Thumbs up mate

Huey: The decison is now made to remain "status quo". I'm getting that feeling a might have been asking more from the boat than what is capable...might be time for an upgrade

Can anybody reccommend a good outboard mechanic to verify the modifications on the Northern Beachs Mona Vale & beyond?

Any oppions on what she might be worth $ ?

As for a mechanic why not try our sponser next time it needs a service or tune - not that far away.

If the motor is running fine and pushing the boat ok I wouldn't be too worried and does so without obvious changes in the colour of the plug deposits or exhaust colour it won't be in a near death position.

Phone a Yammi dealer / mechanic and ask them what the mechanical differences was between the 25 and 30 as you have been told yours has been done. They may tell you it is just a restrictor plate , or that and a rejet of carb or spit out a complete parts list. If they don't want to talk have a look on the internet for the exploded parts diagram for both motors and just tick off the part numbers will give you the same result. Then check which parts yours has.

The manufacturers aren't stupid and unles the model was changed to fill a gap in their line up there was always a part or cost difference between 25 and 30hp otherwise why wouldn't everyone just buy the cheaper 25hp and do the modification. A lot of backyarders believe it is only one part changed but could be piston crown shaps, airbox modifications, carby , exhaiust, port grinding,rev limiter,head shape etc etc.

The only way to know about your motor is to check the part numbers used against the book and what the tuning specs were.

Unless you did the modification it will be hard to tell and loads of people sell boats saying it is a more powerful motor as a sales pitch. Some older models were a simple deal to do. I prefer my motors unmodified as most tinkerers only do half job and it can be at the expense of the longevity of the motor.

It can be very hard to tell the performance difference between a 25 and 30hp in motors unless you have them side by side same day same boat so it is hard to prove. Could mean faster top speed or just gets to the same top speed faster.

Putting little motors on a dyno would be a waste of time and money unless it is a race motor and then a wot run and a GPS does the same as they have exact prop performance data to compare.