A reliable ally for tightening knots
when using thick line to target bluefin tuna
Studio Ocean Mark
‘Ocean Notter OK230BM’

For tying thick lines to catch large fish

In lure fishing for large fish, it is essential to secure the connection between the leader and the PE line, as well as the leader’s attachment to the rings used to mount lures, as firmly as possible. It is vital to tighten the knots firmly without compromising strength. The FG knot is a method favoured by many anglers for joining PE line to a leader in casting fishing, and Studio Ocean Mark’s ‘Ocean Notter OK105H and OK70’ were created to enable this FG knot to be tied quickly and perfectly. This tool ensures that the PE line is wound tightly and evenly around the leader with each turn, minimising unevenness in the weave and enabling a knot that maintains its strength. The OK105H is compatible with PE lines from No. 2 to No. 8, whilst the OK70 is compatible with PE lines from No. 0.6 to No. 3.

The Ocean Notter OK230BM, designed to handle thick PE lines and enable a powerful tightening. It is available in three colours.

These are the Ocean Notter OK105H and OK70. They enable a more secure FG knot for PE lines ranging from No. 0.6 to No. 8. Using them ensures the process runs smoothly.

However, in recent years, situations have arisen where even thicker lines are required. A prime example of this is fishing for bluefin tuna. With stocks having recovered, bluefin tuna have become a target for many anglers. Furthermore, they are growing larger year on year. Consequently, it is now anticipated that lines as thick as PE No. 12 and No. 15 will be required. The leaders to match these PE lines are 270lb, 300lb and 330lb. In such cases, the OK105H has become too small to handle the task comfortably. Furthermore, tightening the knot requires greater force. Consequently, development proceeded on the ‘Ocean Knotter OK230BM’.

Tighten knots securely whilst seated!

When using thick lines of PE No. 12 or above, both tightening FG knots and securing tackle require greater force. Hiromu Sano, a field tester for Studio Ocean Mark with a proven track record of catching numerous bluefin tuna, would use the OK105H for the braiding, whilst for the tightening, he would use two of his original line-winding rods (line-holding rods), holding them with his feet and hands and utilising the strength of his back muscles to tighten the knot with his whole body. However, this method was inefficient and made working on board the boat difficult. He therefore suggested to Studio Ocean Mark that ‘a larger model was needed’. In response to this request, the Ocean Knotter OK230BM was born.

The Ocean Knotter OK230BM was developed following a suggestion from Mr Sano, who has caught numerous bluefin tuna. The comprehensive instructional video below demonstrates how to use it!

Before the OK230BM was developed, Mr Sano reportedly used a line-winding rod he had made himself, holding it with his feet and hands whilst using his whole body to tighten the knot. With the arrival of the OK230BM, however, all of this can now be done right at his fingertips.

Studio Ocean Mark has developed many groundbreaking items essential for anglers over the years. With this latest model, they have not merely made it larger and stronger, but have incorporated a new mechanism that utilises the principle of leverage to allow tightening with minimal effort. This enables the user to tighten the knot whilst seated, after the braiding is complete. Consequently, the user can perform the tightening whilst looking directly at the knot. This has resulted in a more perfect knot.

As it is now larger, it has become much easier to braid FG knots with thick line.

When tightening an FG knot tied with thick line, using the OK230BM allows you to apply strong force by utilising the lever principle, enabling a much firmer tightening. It is said to be capable of applying approximately twice the force.

【Short explanatory video from the 2026 Fishing Show】

A prototype of this OK230BM was unveiled at fishing shows across Japan in the spring of 2026, and many anglers were likely surprised by its performance and the need for such a tool. The production version is finally going on sale. Mr Sano has achieved numerous catches using the knots tied with this Ocean Knotter OK230BM, and it has a proven track record. This is an item that anglers who use thick lines to catch large fish—particularly when targeting large bluefin tuna—should definitely check out.

If you can trust your knot, you can concentrate fully on the fight. When fishing for large fish, it is an ironclad rule to have no doubts whatsoever about the knot. *Photos courtesy of Hiromu Sano

【Comprehensive video guide on how to use the Ocean Notter OK230BM】

Even with thick line, you want to tighten it securely and aim for a perfect knot.

Also excellent for tying rings and hooks!

Furthermore, the tightening action provided by the Ocean Notter OK230BM is also useful when securing the tip of the leader to metal fittings. When targeting bluefin tuna, Mr Sano uses tube knots or Laro knots to attach the leader to the fittings on which the lure is mounted. When securing the leader to these fittings, using a thick leader requires considerable force to tighten the knot. Consequently, many anglers use their whole body to tighten these knots. However, the Ocean Notter OK230BM is equipped with a hook that can be hooked onto the tackle; by hooking rings onto this, you can tighten the knot firmly right at your fingertips. Furthermore, whilst many anglers use fluorocarbon leaders for jigging, thick fluorocarbon makes it even more difficult to tighten the knot securely due to the stiffness of the material. Using the Ocean Notter OK230BM makes tightening these knots effortless. Furthermore, the Ocean Notter OK230BM comes into its own when creating assist hooks using Zylon knots for targeting large fish, as well as when attaching leaders and hooks for bait fishing aimed at big catches. It is sure to be a valuable aid for anglers targeting large fish who use thick lines.

When using thick leaders or reinforced tubing, it can sometimes be impossible to tighten the knot securely onto tackle using arm strength alone. You can rest assured if you use the Ocean Notter OK230BM to tighten it!

【How to use the Ocean Notter OK230BM when attaching a leader to tackle】

In recent years, Mr Sano has been using a line system that involves slipping a Scrum 16 over the knot to minimise the deterioration of the PE line near the leader caused by repeated casting. You can see the knotting method using the Ocean Notter OK230BM in the video below. We highly recommend you take a look.

【FG knot using Scrum 16, suitable for giant bluefin tuna】

Summary: Anglers’ Time Editorial Team