Engine issue under full load

[Looney Toon]

We have a 2012 20 SL 25 logs with a 70HP Yamaha. Yesterday we had 8 adults plus coolers onboard and the bimini up. We were heading down the river toward the Gulf with an incoming tide. I normally keep the engine trimmed completely down while underway. Underway the engine sounded like it was lugging. I tried trimming the engine a bit but it made no difference. It felt like the boat was underpowered but the 70HP is the maximum the pontoon is rated for. Should the heavier loads be towards the back of the pontoon? Any ideas or thoughts?

 

[clrd]

What prop do you have on it. And

Do you remember what your rpms were

 

[Geoffrey & Brenda]

More specifics would help, but that sounds pretty normal to me. We have the 20 SLi 25" tubes and T50 Yamaha. With 2 on board i can get 5800 rpm, add 2 more adults and their cooler, 5200 rpm, add 2 more and it seems like it's way under powered.

The engine has only so much available power, and as you add more weight, more of your tubes are in contact with the water creating more drag, slowing you down.

Moving weight to the stern will help get the nosecones out of the water, but you still have the additional weight onboard. So it comes down to physics, more weight to push, more power is required.

 

[Looney Toon]

It would be the standard prop that came with the motor from the Bennington dealer. Will have to take a look. I normally do look at the RPM's but did not yesterday. I imagine it was all of the factors with a full load plus an incoming strong tide, bimini up and a lot of churning water from the bigger boats coming back from scalloping in the Gulf. If I were boating in a nice calm non tidal lake I probably would have not had the issue to the extent I had yesterday.

It's our first experience with a pontoon and like everyone else we should have gone bigger with more power We have the Amber Yellow and absolutely love it but unfortunately Bennington decided to drop the color.. We get compliments all the time and would hate to trade it in.